RMC-8(+1) Conference, Budapest

21 Sept 2023, 00:20 → 23 Sept 2023, 23:40 Europe/Budapest

room 103 (Central European University, CEU Nador 15 Campus (Budapest, Hungary))

THE FIRST 35 YEARS of REVERSE MONTE CARLO MODELING 
 

Date

21 to 23 September, 2023

Payment of conference fee: 200 EUR

Venue

CEU Nador 15 Campus

15 Nádor utca, Budapest, Hungary

 

_{Photo from https://www.ceu.edu/}

 

Introduction

By 2023 Reverse Monte Carlo (RMC) modelling, a method for modelling structural disorder in liquids, amorphous and crystalline solids,  has been around for 35 years. The first international meeting dedicated to RMC was organised by Robert McGreevy and was held in Studsvik (Sweden) in 1994. In October 2003, we met in Budapest to hold the 2nd RMC Conference. It was there where the participants agreed to hold such meetings every third year. According to this plan, the 3rd RMC and 4th meetings were held in Hotel Normafa, Budapest (Hungary) late September in 2006 and early October, 2009, respectively. As the attendees would remember, the meeting in 2012 had to be transferred in the last minute to another venue within Budapest, Holiday Beach Wellness Hotel, where also our last two meetings, RMC-6 and RMC-7 were held in 2015 and 2018.

 

Just before COVID hit us all, it had been possible to conduct an international meeting on RMC in Kumamoto (Japan) in February 2020: it was the '1st Pan-Pacific Reverse Monte Carlo Conference' -- this event is the '(+1)' indicated in the event title.

As three years has passed since the last RMC meeting, and also, the COVID-situation seems to be advantageous these days, we think it's high time to hold the next international conference on (all the diverse aspects of) Reverse Monte Carlo modelling. 
 

Topics to be covered: anything related to RMC (even remotely). 

• Structure of liquids and amorphous materials;
• Interpretation of powder diffraction data for crystals;
• Software development: new computer codes (RMC, EPSR, PFGui, etc...);
• Related methods: we plan to hold sessions dedicated to EPSR and PDFGui (other suggestions also welcome);
• Extending the applications of RMC: modelling small angle scattering, reflectometry, inelastic scattering, EXAFS, NMR, etc...
• Etc... 
   

 

Conference fee -- set to 200 EUR

We are sorry to announce that for covering the steeply rising costs (of everything, especially in downtown Budapest...), we have to collect a conference fee this year.

 

We seem to have reached an agreement with the verious service providers.  The conference fee will be 200 EUR. It will cover the rental of the conference room and coffee breaks.

 

We kindly ask to pay the conference fee by bank transfer. We apologise for that we are not able to deal with card payments. Details concerning payments (account number, etc...) will be available soon. Our institute, the Wigner Research Centre, will send a 'pro-forma' invoice to each registered participant, so that you can proceed with the actual money transfer the way it is most convenient for you.

Deadline: 31 July 2023.

Accommodation

As indicated above, instead of a 'conference hotel', the 2023 event will take place in a proper conference room, in downtown Budapest. 

We kindly ask participants to organise for their own accomodations -- there should be no problem to find one via the usual channels (Booking.com, etc...).

We are, of course, happy to provide help in finding a place to stay.

 

Previous conferences

7(+1)the RMC meeting in 2020 (a.k.a. the '1st PanPacific Reverse Monte Carlo Conference')

7th RMC Conference in 2018 

6th RMC Conference in 2015; for the corresponding Special Issue, please visit the webpages of  Physica Scripta

5th RMC Conference in 2012; for the corresponding Special Issue, please visit the webpages of JPCM

4th RMC Conference in 2009; for the corresponding Special Issue, please visit the webpages of JPCM 

3rd RMC Conference in 2006; for the corresponding Special Issue, please visit the webpages of JPCM

2nd RMC Conference in 2003; for the corresponding Special Issue, please visit the webpages of JPCM 

 

 

 

Thursday, 21 September

08:30 Welcome registration

Th1

1 Opening

Welcome to RMC 8( +1) conference after the long time in Budapest ...

Speaker: Laszlo Pusztai (Wigner RCP)

2 RMC is 35 – How has it changed total scattering/pair distribution function analysis?

When the original Pusztai & McGreevy RMC paper was published in 1988
we were at a turning point in the use of total scattering and pair
distribution functions (PDFs) in structural analysis. This talk examines
to what extent their paper was a watershed, transforming not just total
scattering analytical methods but also the way that we thought about
structure, and disordered structure in particular. I will first spend
some time explaining the time-line leading up to 1988 and will place the
Pusztai & McGreevy work in the context of what else was happening at the
time. This will set the scene for the second part of my talk where I
will discuss what followed, highlighting some of what has been achieved
since and providing a personal perspective as to what is still to be
attempted.

Speaker: David Keen

3 Short range order and stability of amorphous tellurides

Te-rich amorphous Ge-Sb-Te alloys were investigated by diffraction techniques and EXAFS. Structural models were obtained by fitting all datasets (5 for each sample) simultaneously. The results showed that the alloys are chemically ordered (number of heteronuclear bonds maximized) and obey the 8-N rule. An overview of literature data shows a strong correlation between the glass transition temperature of amorphous tellurides and their average coordination number. The Ge-Sb-Te alloys investigated fit remarkably well in this trend.

Speaker: Pál Jóvári (MTA Wigner FK)

Jovari_RMC_conference2023_presentation_compact.pdf

4 Advances in modelling X-ray absorption spectroscopy data using reverse Monte Carlo

Modern extended X-ray absorption fine structure (EXAFS) analysis is based on multiple-scattering calculations. Those calculations are carried out for fixed atomic configurations and proper account of the thermal and static disorder, corresponding to well-defined pair and higher-order distribution functions, can be obtained using different methods. The application of the Reverse Monte Carlo (RMC) method is able to provide tridimensional models of the atomic structure compatible with a given set of experimental data, producing useful and consistent structural models. This method has been proposed and applied also to EXAFS data by several authors in the last 25 years and has been fully implemented in the framework of the RMC-GnXAS method for EXAFS data-analysis. Here we present the extension and application of this method to multiple-edge studies of molecules, crystalline solids and liquids, including the long-range constraints provided by other techniques (e.g. diffraction). The potential and possible weaknesses of the RMC method are discussed, as well as the importance of accounting for the effect of noise levels in XAFS data. Results of RMC refinements are reported for several exemplary cases including Br2 and GeI4 molecular gases, crystalline Ge and AgBr, amorphous Ge and liquid AgBr. Those applications show the general interest for this method, and the importance of combining multiple set of data for improving the accuracy of the structural refinement both at short and long range. Recent developments and applications showing direct effects of triplet correlations will be also briefly discussed.

Speaker: Andrea Di Cicco (School of Science and Technology - Physics Division University of Camerino)

10:40 Coffee break

Th2

5 Combining Reverse Monte Carlo Analysis of X-ray Scattering and Extended X-ray Absorption Fine Structure of Very Small Nanoparticles

Reverse Monte Carlo (RMC) simulations enable the analysis of X-ray Scattering (XS) data as well as Extended X-ray Absorption Fine Structure (EXAFS) spectra data via partial pair distribution (pPDF) functions obtained from a physical, structural model. In case of nanoparticles and scattering data this approach suffers from the termination of the pPDF’s due to the finite size of the particles. This produces artifacts in the computed scattering intensity due to the long-range probing distance of scattering which are eliminated by using the Debye scattering equation (DSE) for computing the scattering intensity from a particle model. Computational efficiency is provided by binning the distance distribution of atom pairs in the DSE. Simultaneous refinement of XS data and EX-AFS spectra of small nanoparticles are thus enabled using a mutual structural model. This method allows the self-consistent extraction of complementary information on local structure contained in EXAFS and long-range order in XS data. In this contribution we describe this novel method using XS and EXAFS data of nanocrystalline LaFeO3 [1]. Additionally, results for SnO2 are presented.

[1] M. Winterer and J. Geiß, Combining reverse Monte Carlo analysis of X-ray scattering and extended X-ray absorption fine structure spectra of very small nanoparticles, J. Appl. Cryst. 56 (2023) pp. 7; doi.org/10.1107/S1600576722010858

Speaker: Prof. Markus Winterer

6 Structural complexity in amorphous calcium carbonate

Amorphous calcium carbonate (ACC) is an important metastable precursor for marine organism biomineralisation processes. However, the origin of the metastability of ACC is currently not well understood. Here, we use hybrid reverse Monte Carlo (HRMC) to generate atomistic models of ACC, driven by both experimental total scattering measurements [1] and interatomic potentials [2].

Using a recently-developed algorithm [3], we inverted the Ca—Ca pair correlation function from our HRMC model to obtain the effective Ca—Ca interaction potential. The form of this interaction resembles a Lennard-Jones—Gaussian (LJG) potential, characterised by two competing length scales [4]. This competition is known to frustrate crystallisation. The parameterisation of the LJG potential for ACC highlights the origin of geometric frustration in this system; namely, two distinct carbonate-bridging motifs.

Simulations driven by this effective Ca—Ca potential recover the two dominant characteristics of the ACC structure model: a heterogeneous structure, and a resilience to crystallisation. We therefore attribute both features to the geometric frustration encoded in the effective interactions between calcium ions.

References

[1] Michel, F. M., MacDonald, J., Feng, J., Phillips, B. L., Ehm, L., Tarabrella, C., Parise, J. B. & Reeder, R. J. (2008). Chem. Mater. 20, 4720—4728.
[2] Raiteri, P., Gale, J. D., Quigley, D. & Rodger, P. M. (2010). J. Phys. Chem. C 114, 5997—6010.
[3] Stones, A. E., Dullens, R. P. A. & Aarts, D. G. A. L. (2019). Phys. Rev. Lett. 123, 098002.
[4] Dshemuchadse, J., Damasceno, P. F., Phillips, C. L., Engel, M. & Glotzer, S. C. (2021). Proc. Natl. Acad. Sci. U.S.A. 118,

Speaker: Thomas Nicholas (University of Oxford)

7 Changes in atomic structures on a Gd65TM35 glass by cryogenic rejuvenation

Rejuvenation in glasses is defined as an excitation to a higher energy state by an external stress. Ketov et al. reported a rejuvenation effect in metallic glasses (MGs) by a temperature cycling between room and liquid N$_2$ temperatures [1]. Hufnagel reviewed such a cryogenic rejuvenation, and suggested that non-affine deformation must be caused on an atomistic length scale [2]. We carried out a high-energy x-ray diffraction (HEXRD) and an elementally-selective anomalous x-ray scattering (AXS) on a Gd$_{65}$Co$_{35}$ MG. We analyzed these data by a reverse Monte Carlo modeling, and found distinct structural changes around both the Gd and Co atoms [3]. Subsequently, we performed the same experiments and analyses on a Gd$_{65}$Ni$_{35}$ MG, and closely similar results were realized in partial structures. In this presentation, we will report the structural changes of the Gd$_{65}$TM$_{35}$ MG alloys by the cryogenic rejuvenation in detail.

[1] S. V. Ketov et al., Nature 524, 200 (2015)
[2] T. C. Hufnagel, Nature Mater. 14, 867 (2015)
[3] S. Hosokawa et al., to be submitted to Sci. Adv.

Speaker: Prof. Shinya Hosokawa (Kumamoto University)

8 Structural characterization of iron phosphate glasses by neutron diffraction in combination with Reverse Monte Carlo simulation

The final phase of the nuclear fuel cycle involves a critical task: finding suitable matrices and materials to safely incorporate and immobilize high-level radioactive waste 1. Borosilicate glasses have been widely used for high-level nuclear waste immobilization 2. However, iron phosphate and lead iron phosphate glasses are also functional materials that are considered to be economical alternatives to borosilicate glasses for nuclear waste immobilization 3, because these are good solvents for heavy metal ions and exhibit excellent leaching resistance in both acidic and neutral medium. The chemical durability of phosphate glasses can be enhanced significantly by adding Fe2O3 in the glass network; the addition of these metal oxides replaces the easily hydrated –P–O–P– bonds by more hydrate resistant –M–O–P– bonds, where M are metal cations.
Iron phosphate glasses containing 25 to 40 mol% Fe2O3 were prepared by melt quenching technique. Density increases from 2.8 to 3.2 gcm-3. The glass transition, crystallization and liquidus temperatures were determined by differential scanning calorimetry analysis. The ionic packing fraction show small variation while the glass forming tendency decreases significantly with an increase in Fe2O3 concentration in the phosphate network. The Reverse Monte Carlo simulation of neutron diffraction datasets were used to calculate the partial atomic pair distributions and coordination environments in iron phosphate glasses. The most probable P-O and Fe-O bond distances are 1.50 Å and 1.85 Å respectively. Fe exists mostly in 3+ oxidation state with little or no concentration of Fe2+. It is possible that some results reported in the literature that Fe2+ and Fe3+ co-exist in the iron phosphate network and that the relative concentration of Fe2+ in the final glasses increases with an increase in melting time and temperature are erroneous, and this effect could be due to the incorporation of Al3+ in the melt from the slow leaching of alumina crucibles that were used for glass synthesis by previous investigators.
The bond angle distribution in the glass network shows the peaks in the angle ranges: 75-88º and 95-116º for O—Fe—O and O—P—O linkages, respectively. The O—O—O bond angle distributions has a maximum at 60o. The Fe-O co-ordination is in the range: 3.60-4.57 and P-O co-ordination is in the range: 3.09-3.35.

References:

[1] J.D. Vienna, Nuclear waste vitrification in the United States: recent developments and future options, International Journal of Applied Glass Science 1 (2010) 309-321.
[2] C.P. Kaushik, R.K. Mishra, P. Sengupta, Amar Kumar, D. Das, G.B. Kale, Kanwar Raj, barium borosilicate glass – a potential matrix for immobilization of sulfate bearing high-level radioactive liquid waste, Journal of Nuclear Materials 358 (2006) 129-138.
[3] D. Day, C. Ray, C. Kim, Final Report: Iron Phosphate Glasses: an Alternative for Vitrifying Certain Nuclear Wastes, Project No, DEFG07 e96ER45618, (2004).

Speaker: István Tolnai (CER)

12:50 Lunch

Th3

9 RMCProfile: Past, Present and Future

Many of the useful materials that make modern life possible are crystalline. Quartz keeps our watches on time, perovskites are widely used in consumer electronics and solid oxide fuel cells may help to power the future.

The importance of local structure and disorder in crystalline materials is increasingly being recognised as a key property of many functional materials. From negative thermal expansion to solid state amorphisation and the 'nanoscale' problem to improved fuel cell technology, a clear picture of the local atomic structure is essential to understanding these phenomena and solving the associated problems.

Here I will discuss the program RMCProfile, which was built on top of the original RMCA program and that we have been developing over the past two decades to use total scattering and reverse Monte Carlo to study disordered materials. As the materials and details being studied become more complicated increasing multiple data types, together with modelling approaches, need to be combined and RMCProfile can help you achieve this. Here I will introduce why we developed the program, give a recent example to illustrate the sort of useful information you can gain using the total scattering and the RMC method and then brief describe the planned future developments.

Speaker: Matt Tucker (Oak Ridge National Lab')

10 Reverse Monte Carlo modeling of ZrO2-doped Li$_2$O–SiO$_2$-based multi-component glasses using anomalous X-ray and neutron scattering data

Molecular dynamics–reverse Monte Carlo (MD–RMC) method was applied to ZrO$_2$-doped Li$_2$O–SiO$_2$-based multi-component glass, a mother material for high-strength glass ceramics, using anomalous X-ray and neutron scattering data in order to construct a structural model of this glass. Since anomalous X-ray scattering data provide local structural information around Zr, reliable structural model around Zr (~5 at%) was succeessfully obtained by the MD–RMC method.
We found that a significant fraction of edge-sharing structures was formed around Zr–O and Li–O polyhedra, resulting in a densely packed configuration of O atoms. This configuration was manifested by a very sharp principal peak in the neutron scattering data. Our model indicates that the Zr and Li ions are incorporated in the glass as distorted ZrO$_6$ octahedra and distorted LiO$_4$ tetrahedra, respectively. These structural features are discussed in terms of the crystallization behavior of this material.

Speaker: Koji Kimura (Nagoya Institute of Technology, National Institute for Materials Science, Japan Synchrotron Radiation Research Institute)

11 RMCProfile7 – a big box Pair Distribution Function modelling

Nowadays, scientists have to work on more and more complicated materials. Description of crystal structures in terms of average structure as obtained from Bragg diffraction data analysis is no longer enough to understand material properties. Pair Distraction Function (PDF) is its natural extension and allows us to look deeper into the real (= both local and average) structure of materials. Big box modelling of PDF is currently the best method to understand local arrangement and/or short-range correlations of atoms without assuming any symmetry related constrains.
In the talk I will present the most recent development in the field of RMCProfile7 program and also some successful examples where only by using those new developments in the code new insight into the local structure could have been obtained.
The beauty of RMCProfile7 program and large box modelling is that it combines average structure modelling and local structure disorder and enables to find global minimum which gives a good picture of both avenge and local view of the same structure.
The most recent development of RMCProfile7 includes:
• Multiple phase refinement – useful for complex or mixed phases
• Multiples of datasets (i.e. multiple of Bragg datasets, joint X-Ray and neutron refinements, different PDF representations)
• Real space PDF calculation as a back Fourier transform of reciprocal space data – very useful for X-Ray PDF and lower instrumental Qmax datasets
• Variety of constraints (minimum distance, moveout) and restraints (bond valence sum; broad variety of potentials – bond, angles, torsion angles, inversion angle, planarity, planar rings; tails) which enables more physical atomic configurations or fasted convergence to global minimum
• Molecular type moves (rigid body or molecular)
RMCProfile7 is freely available on https://rmcprofile.pages.ornl.gov/

Speaker: Wojciech Slawinski (University of Warsaw)

15:40 Coffee break

Th4

12 A NMR-Driven Reverse Monte Carlo Study of Sodium Borate Glasses Boosted with Machine Learning

In sodium borate glasses, boron atoms can be found in triangles (BO3) or in tetrahedral (BO4) units, which population can be easily quantified with the help of NMR spectroscopy.[1] These two speciations of boron generates the boron’s anomaly, which is a non-linear evolution of properties upon the addition of sodium oxide.[2] In addition, a large fraction of boron are involved in superstructural units like boroxol or pentaborate rings.
However, those units remain difficult to identify in experimental NMR spectra and more sophisticated 2D techniques (such as MQMAS) are generally required. Howerver, modern NMR computational tools make it now possible to model NMR spectra from MD simulations and thus can significantly improve the interpretation of experimental data.[3]

In this work, we investigate theoretically and experimentally the structure of sodium borate glasses using 11B and 23Na NMR combined with molecular dynamics (MD) simulations and neutron diffraction. Comparison of classical MD (CMD) with ab-initio MD (aiMD) shows that only aiMD produces structural models with a non-negligible fraction of super-structural
units but still below the one determined by two-dimensional 11B MQMAS NMR
spectroscopy.

In order to improve our structural models, in particular to include a larger fraction of superstructural units, we develop a hybrid reverse monte carlo (HRMC) scheme for accounting for NMR and neutron data, including a MD force-fields and implementing a simulated annealing approach for accelerating the search of new optimized structures. The
fraction and the form of superstructural units is an adjustable parameter and we observe that neutron data are not sufficiently sensitive to discriminate the various structural models generated, in contrast to 11B NMR for both BO3 and BO4 units (i.e., ring and non-rings species). Simulated 11 B and 23 Na 2D MQMAS NMR are found to be in good agreement
with experiments but the DFT-GIPAW NMR calculations computational cost limits the size of systems that can be studied (from 500 to 1000 atoms). In order to overcome this limitation, we employ a recently developed a Machine Learning (ML)[4] approach for computing NMR shifts and it first applications to borate glasses will be presented.

[1] C. Lee, S. K. Lee, J. Non-Cryst. Solids, 555, 120271 (2021)
[2] K. Vignarooban, P. Boolchand, M. Micoulaut, M. Malki, et W. J. Bresser, EPL Europhys. Lett. 108, 56001 (2014).
[3] T. Charpentier, M.C. Menziani, A. Pedone, RSC Adv. 3, 10550-10578 (2013)
[4] Z. Chaker, M. Salanne, J-M. Delaye, T. Charpentier, Phys. Chem. Chem. Phys. 21, (2019) 21709

Speaker: Dr Thibault CHARPENTIER (CEA)

13 RMC modelling of the high-k dielectric bismuth silicate glass

The bismuth silicate (Bi$_2$SiO$_5$) glass possesses some exceptional dielectric properties, including a high dielectric constant that is significantly larger compared to most other glasses. To gain insight into this behavior, we conducted a comprehensive analysis of the glass structure using a combination of high-energy X-ray scattering, X-ray absorption spectroscopy, and RMC modeling with a further investigation of the atomic-scale order by persistence homology (PH) analysis. Furthermore, based on Si NMR data, constraints were established for the SiO4 tetrahedra and their connectivity. The analysis revealed that the majority (approximately 90%) of the SiO$_4$ tetrahedra exist as $Q^2$ species, forming one-dimensional chains within the structure.
However, modeling the glass structure poses a challenge due to the peculiar electronic structure of Bi. In comparable crystalline phases, Bi is present as either a BiO$_5$ or BiO$_6$ polyhedron, in which all the oxygen atoms are constrained to one hemisphere of the coordination shell, while the other side is occupied by an electron lone pair. This arrangement results in a substantial atomic-level polarizability, which contributes to the large dielectric constant observed in the crystal phase [1,2]. Note that the Bi$_2$SiO$_5$ crystal is a metastable compound that can only be found in a nonequilibrium phase diagram. Consequently, samples of Bi$_2$SiO$_5$ are fabricated through the crystallization of Bi-Si-O glasses.
Remarkably, our analysis demonstrated that similar features can be identified within the glass structure as well. The experimental data is compatible with a structure composed of BiO$_x$-polyhedra-rich regions dispersed throughout a network of disordered SiO4 tetrahedral chains. The details will be presented in this presentation. Overall, our findings shed light on the structure of the Bi$_2$SiO$_5$ glass and its correlation with its remarkable physical properties, particularly the remarkably high dielectric constant.

References
[1] H. Taniguchi et al., Angewandte Chemie Int. Ed. 52 8088-8092 (2013).
[2] H. Taniguchi et al., Phys. Rev. Mat. 2 04560 (2018).

Speaker: Jens Stellhorn (Nagoya University)

14 Quantification of Cation Pairs in Cobalt Iron Oxide Nanoparticles by RMC Analysis to Identify Structure-Activity Relationships

Complex oxides like Co_3-xFe_xO₄ spinel nanoparticles are promising heterogenous catalysts. However, the identification of quantitative structure-activity relationships of high specific surface area materials like nanoparticles is challenging. Furthermore, the distribution of cations on tetrahedrally and octahedrally coordinated sites in the spinel crystal adds an additional layer of structural complexity.

We present a Reverse Monte Carlo study using rmcxas$^{[1]}$ where a mutual structural model of Co_3-xFe_xO₄ spinel is refined simultaneously by EXAFS datasets form the Fe and Co K-edges. Moreover, the refined model differentiates between tetrahedrally and octahedrally coordinated cation absorber sites to enable the identification of the cation distribution.

We find that the Co_3-xFe_xO₄ nanoparticles consist of a spinel structure where tetrahedrally and octahedrally cation sites are occupied by both elements and the overall cationic distribution is strongly influenced by the overall elemental composition. Frequencies of the cation pairs Co$\mathrm{_{oct}}$-Co$\mathrm{_{oct}}$ and Co$\mathrm{_{oct}}$Co$\mathrm{_{tet}}$ are extracted from the refined structural model and directly correlate to the catalytic performance in selective oxidation of 2 propanol.$^{[2]}$

[1] Winterer, M. Reverse Monte Carlo Analysis of Extended X-Ray Absorption Fine Structure Spectra of monoclinic and Amorphous Zirconia. J. Appl. Phys. 2000, 88, 5635−5644.

[2] Geiss, J.; Falk, T.; Ognjanovic, S.; Anke, S.; Peng, B.; Muhler, M.; Winterer, M. Atom Pair Frequencies as a Quantitative Structure-Activity Relationship for Catalytic 2-Propanol Oxidation over Nanocrystalline Cobalt-Iron-Spinel. J. Phys. Chem. C 2022, 126, 10346−10358.

Speaker: Jeremias Geiss (University of Duisburg-Essen)

15 Hydration properties of monosaccharide molecules

Monosaccharides are the basic building blocks of carbohydrates, which are considered as one of the most essential biomolecules with playing principal roles in several biological processes such as molecular recognition, and structural stabilization and modification of proteins and nucleic acids that can act as cryoprotective molecules for living cells. [1]

Although monosaccharides are generally considered hydrophilic compounds, they have substantial hydrophobicity that varies with their structure. The competition of the intramolecular H-bonds with the intermolecular ones, which are formed between the monosaccharide and the water molecules, along with the hydrophobic interactions, determine the solvation shell of these molecules.

In this presentation, we consider various isomers of simple sugars (D-glucose, D-galactose, D-mannose and D-fructose) [2] whose molecular structures are very similar, yet their basic properties for example solubilities in water can be rather different. We calculated different properties that characterize the monosaccharide’s molecules’ hydration and reveal their differences. These include, among others the average number of acceptor and donor H-bonds, the average length of acceptor and donor H-bonds, and the properties of three and four-coordinated water molecules around carbohydrate molecules. Using classical and ab initio molecular dynamics simulations provides a very strong base for our results.

The main novelty is the quantitative characterization of the hydration shell (hydrophilic and hydrophobic) of the monosaccharides by calculating the number of water molecules below and above the plane of the studied monosaccharide molecules. The largest difference was found between the two isomers of the same monosaccharide, which is the D-glucose. [3]

References

[1] R. A. Dwek, Chem. Rev. 96, 683, 1996
[2] T. L. Mega, S. Cortes, R. L. Van Etten, J. Org. Chem. 55, 522, 1990
[3] I. Bakó, L. Pusztai, Sz. Pothoczki, https://arxiv.org/abs/2308.03653

Speaker: Szilvia Pothoczki (Wigner FK)

POSTER th: Posters

Poster session

16 Amorphous Solid State Electrolyte Li7P2S8I - Structural Investigations for two States

Li7P2S8I, an amorphous solid state elecrolyte reveals an increase in Li+ ion conductivity when tempered.The increase in conductivity of 0.8 mS/cm (room temperature) up to 4.6 mS/cm is shown with impedance spectroscopy [1]. The tempering temperature (180°C) is 10°C lower than the melting temperature.

Despite not overcoming the melting temperature, the x-ray diffraction pattern reveals a significant difference between the non-tempered and the tempered state. This difference might be the reason for the measured increase in conductivity.

For determination of the structure, Reverse Monte Carlo simulations are used with x-ray scattering and EXAFS (K edge of S, HiSOR) measurements as boundary conditions. Additional structural information as PS4 Tetrahedrons (by 31 P NMR measurements [3]) are partly included in the simulations.

References:
[1] Spannenberger, S.; Miß, V.; Klotz, E.; Kettner, J.; Cronau, M.; Ramanayagam, A.; di Capua, F.; Elsayed, M.; Krause-Rehberg, R.; Vogel, M.; Roling, B., Solid State Ionics 341, 115040 (2019).
[2] McGreevy, R. L.; Pusztai, L., Molecular Simulations 6, 359 - 367 (1988).
[3] Miß, V.; Neuberger, S.; Winter, E.; Weiershäuser, J. O.; Gerken, D.; Xu, Y.; Krüger, S.; di Capua, F.; Vogel, M.; Schmedt auf der Günne, J.; Roling, B., Chem. Mater 34, 7721 - 7729 (2022).

Speaker: H. M. Wenzel (Philipps-Universität Marburg, Germany)

17 Characterizing reciprocal space resolution of 2D XRD setup at the P21.2 beamline

The Swedish Materials Science beamline (SMS) located at the PETRA III synchrotron storage ring (DESY Hamburg, DE) is dedicated to materials research using high-energy X-rays. The beamline consists of an inline branch (P21.2) and a side branch (P21.1), which are operated in parallel and are optimized for a combination of techniques and broad band diffraction, respectively. The inline branch P21.2 operates in the energy range of 40 - 150 keV and is designed for the combination of WAXS, SAXS, and Imaging techniques. Due to high-energy photon beam available at the P21.2 it is perfectly suited for the investigation of highly disordered materials by means of pair distribution function (PDF). The PDF, which characterizes material’s atomic structure in real r-space, is obtained by a sine Fourier transform of the structure factor S(q), which refers to X-ray scattering power of a given material in reciprocal q-space. The quality of PDF is determined by the coverage of reciprocal space (q-range) and resolution (dq). It is impossible to improve both parameters simultaneously since there is an inverse relationship between them. Performing an X-ray scattering experiment with high energy photon beam using a large two-dimensional (2D) detector positioned at a short sample-to-detector distance helps to acquire scattering data up to large magnitudes of wave momentum transfer vector q, which implies a good resolution of PDF in lower range of r-space. This is fine for materials which are having structures with short range order. However, it poses a challenge for materials with larger degree of structural order such as nanocrystalline materials.
In this contribution we present systematic study of reciprocal space resolution of 2D XRD setup implemented at the P21.2 beamline. Beam size, sample thickness and sample-to-detector distance were identified as key parameters, mostly affecting reciprocal space resolution. Few series of 2D XRD patterns were taken on powder LaB6 standard sample with a monochromatic photon beam having energy of 81.84 keV. Beamsize (square profile) was set to four distinct sizes 0.1, 0.3, 0.5 and 1.0 mm. Sample thickness was set to 0.4, 1.0, 1.5 and 2.0 mm. Sample-to-detector distance was changed from 460 to 1800 mm (10 values). Scattered photons were acquired by 2D detector VAREX XRD4343CT (2880 x 2800 pixels, pixel size 150 μm x 150 μm, 16bit intensity resolution). Altogether 160 (4x4x10) patterns were acquired and used in analysis. Each 2D XRD pattern was radially integrated, and its peak profiles were analyzed with pseudo-Voigt function. Instrument resolution function, i.e. variation of the peak full-width at half-maximum with Bragg angle 2theta, was investigated as a function of the beam size, sample thickness and sample-to-detector distance.

The Authors gratefully acknowledge the contribution of the Slovak Research and Development Agency under the project APVV-21-0387.

Speaker: Ms Ravneet Kaur (Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovakia)

18 Modeling angular resolution of the instrument P21.2 at PETRA III

The angular resolution in the case of angular dispersive X-ray (XRD) diffraction in transmission geometry is significantly influenced by parameters such as the size (cross-section) and divergence of the photon beam, its degree of monochromaticity, the dimensions, geometry of the sample, and the arrangement of the experiment. This work focuses on characterizing the angular resolution of the instrument P21.2 at the PETRA III synchrotron radiation source in DESY Hamburg (DE). The characterization of angular resolution was performed for an experimental setup corresponding to XRD diffraction in transmission geometry using a two-dimensional (2D) detector VAREX XRD4343CT.

In the first part of the work, a series of 2D diffraction records were analyzed, which were obtained on a calibration sample of LaB$_6$. The distance between the reference sample and the 2D detector was systematically varied in the range from 460 to 1800 mm. The photon beam energy was 81.8 keV, its size was 1×1 mm$^2$, and the sample thickness was 1 mm. A relationship between the angular width of diffraction maxima of the LaB$_6$ reference sample as a function of the diffraction angle $2\theta$ and the distance between the sample and the 2D detector was determined by fitting the measured data.

In the second part of the work, attention was given to the theoretical modeling of the experimentally acquired data. A simple model describing a single-scattering event of diffracted photons based on kinematic diffraction theory was proposed. Based on numerical simulation of the model using a Monte Carlo method, theoretical profiles of angular resolution were calculated depending on the parameters used in the diffraction experiment. The obtained results indicate very good agreement with experimental data.

Speaker: Mr Peter Dubecký (Pavol Jozef Safarik University in Kosice, Faculty of Science, Institute of Physics)

19 Reverse Monte Carlo Modeling for Catalyst Nanoparticles in Polymer Electrolyte Fuel Cells by High-energy X-ray Diffraction

Polymer electrolyte fuel cells (PEFCs) consist of a gas diffusion layer (GDL) and an electrode on each side, and a polymer electrolyte membrane (MEA) between the electrodes. The main components of the MEA are catalysts, electrolyte membranes and electrodes. In this study, the local atomic structures of catalytic nanoparticles in MEA were investigated by high-energy X-ray diffraction and reverse Monte Carlo (RMC) modeling. The purpose of this study is to show guidelines for improving the performance of the PEFCs that contribute to industry by clarifying the differences in each catalyst structure and linking them with catalyst performance such as catalytic activity and catalyst durability.
In this conference, we report the structural work on the platinum-cobalt alloy nanoparticles-supported carbon catalyst TEC36F52 (manufactured by TANAKA KIKINZOKU KOGYO K.K.). Although this sample is a commercial product, it is important to investigate its structure because it can be used as a standard sample for evaluating various catalyst samples in the future.
RMC modeling based on the structure factor S(Q) obtained from high-energy X-ray diffraction is suitable to determine the 3-dimensional (3D) atomic structures of nanoparticles. High-energy X-ray diffraction measurements were performed using a two-axis diffractometer at the beamline BL04B2 in SPring-8; the energy was used 61.4 keV corresponding to 0.202 Å in wavelength. For the PtCo nanoparticle studied here, the initial configuration for the RMC modeling is a spherical shape with 2315 particles (Pt: 1744, Co: 571) and about 4 nm in diameter based on the fcc bulk crystal structure. RMC fittings for the experimental S(Q) profiles were performed to obtain the 3D structural models using RMC_POT software. The obtained structural model shows that the average interatomic distance is larger on the surface than in the interior, and the distribution of Co atoms is also altered. These structural features might be involved in the differences in catalytic activity.
This research approach is expected to accelerate the creation of new catalysts for fuel cells by providing local atomic-scale structural information. It is also important to create the database of atomic arrangement structure data that is the basis of material design and material research.
In this conference, the data recorded from the other commercial catalyst samples and the actual catalyst samples which is used in the fuel cell vehicle (FCV) will also be presented.
This work was performed under the NEDO FC-Platform project.

Speaker: Yuki Mizuno (Japan Synchrotron Radiation Research Institute)

20 Reverse Monte Carlo modeling of B2O3 glass based on high-energy X-ray total scattering data

We performed reverse Monte Carlo (RMC) modeling of B2O3 glass based on high-energy X-ray total scattering data. In the B2O3 glass, the so-called boroxol rings are fromed, which are the main structural unit of the glass. Previous studies [1-3] have performed computational modeling of the three-dimensional structure of B2O3 glass, but it was difficult to achieved the expected ratio of boroxol rings, which is typically 65-80%. In this study, dummy atoms were placed at the center of the boroxol rings to enhance the constraint for maintaining their shape. This prevents the collapse of the boroxol rings during the RMC simulation.

We confirmed that the RMC model well reproduced the experimental structure factor. The validity of the three-dimensional structure was confirmed by the ratio of the boroxol rings, coordination numbers, angle distributions, ring size distributions, and void volume. Our accurate structural model will contribute to understand the modification of boroxol rings manifeseted by borate anomaly in alkali borate glasses.

REFERENCES
1. M. Fábián et al., J. Non-Cryst. Solids 356, 441 (2010).
2. A. Takada et al., J. Phys.: Condens. Matter 7, 8693 (1995).
3. E. Kashchieva et al., J. Non-Cryst. Solids 351, 1158 (2005).

Speaker: Koichi Hayashi (Nagoya Institute of Technology, Japan Synchrotron Radiation Research Institute)

21 Simulation of Air Scattering Contributions in X- ray Diffraction Experiments Aiming for Precise Data Correction

In structure analysis of condensed matter by way of X-ray scattering experiments
precise treatment of background intensity is usually negligible so long as crystals
are probed, as their structure information is concentrated in sharp, highly intense
Bragg-reflexes. In less ordered systems such as liquids, glasses and amorphous
solids in general these sharp reflexes are absent and the scattered intensity
carrying the structure information is spread continuously along the diffraction
angle and mixes with the background.
In order to draw information from such scattering experiments a meticulous
analysis and extensive reduction of background intensity is necessary. Accordingly
great effort is undertaken to grasp and separate the various contributions to
background intensity. [1] This is especially relevant when the data is to be used
as constraint in the modeling of investigated systems, e.g. by RMC Simulations.
Part of this unwanted background is intensity scattered by air, as it is not
always feasible to evacuate the experimental setup. The air scattered intensity
is experimentally only directly accessible in a setup without an absorbing and
scattering sample present. Similarly, this intensity is not equal to the air
scattering contribution in presence of a sample, e.g. due to the sample’s absorption
of primary intensity. Therefore it is only a crude approximation to use the
measured air scattering intensity for background correction directly.
In this ongoing work, a model is derived to predict air scattered intensity in
presence of the sample for a typical experimental environment at a synchrotron
beamline. The model is built using the Thomson scattering equation and
atomic form factors as theoretical foundation. From the experimental setup a
general geometric model of the beam path is deduced. Furthermore setup-specific
features in the beam path are regarded as examples that may heavily influence
the measured intensity curves, most prominently the shadow of a beam stop cast
onto an area detector.
References
[1] H. E. Fischer, A. C. Barnes and P. S. Salmon, Reports on Progress in Physics
69, 233 (2006)

Speaker: J. H. Thimm (Philipps-University, Marburg, Germany)

22 Structural analyses of amorphous Si-doped In2O3

Introduction
In recent years, the development of the Internet of Things (loT) has made our lives more convenient, while the power consumption of semiconductors has increased rapidly. To solve this problem, the semiconductors research has conducted to save energy through miniaturization, but new thin-film semiconductor materials are required for further expansion. Amorphous In2O3 thin films have been used in flexible substrate displays because of its excellent electrical properties and high transmittance in the visible light range but it is also characterized by thermal instability. The amorphous structure can be maintained by doped various elements such as Si elements, but it doesn’t clarify how this contributes to the stability of the structure. In this study, we focus on Si-doped In2O3 (ISO) and discuss its thermal stability using a combination of quantum beam diffraction measurement and computer simulation.

Method
The ISO samples with different weight ratios of SiO2 (0, 1, 3, 5, and 10 wt.% Si) were synthesized unheated and heated at 600 ℃. The X-ray diffraction measurements of ISO were performed at the BL04B2 beamline of SPring-8.

Results and discussion
It is confirmed that the S(Q) of heated ISO0, 1, 3, 5 show Bragg peaks while ISO10 remains amorphous after heat treatment. This beharivour suggests that the addition of SiO2 improves the thermal stability of In2O3.The In–In correlation peaks are observed around 3.2 ~ 4.1 Å, suggesting that the formation of different InOx–InOx polyhedral connections, probably by not only corner-sharing, but also edge-sharing of InOx polyhedra.

Speaker: Yuta Shuseki (Kyoto university)

Friday, 22 September

Fr1

23 Cd(CN)2: negative thermal expansion in a structural spin-ice

Cadmium cyanide exhibits the strongest persistent isotropic negative thermal expansion (NTE) effect of all known materials [1,2]. Structural studies of the material are complicated by a combination of extreme x-ray sensitivity [2], the prohibitively large neutron absorption cross-section of natural-abundance cadmium, and the presence of cyanide orientational disorder [3], which is temperature dependent [4]. This talk will summarise some of our recent neutron scattering measurements of 114Cd(CN)2, which are providing insight into the NTE mechanism in Cd(CN)2. Our analysis includes the use of reverse Monte Carlo refinements of neutron total scattering data.

[1] Coates & Goodwin, Mater. Horiz. 6, 211 (2018)
[2] Coates et al., Dalton Trans. 47, 7263 (2018)
[3] Goodwin & Kepert, Phys. Rev. B 71, 140301 (2005)
[4] Coates et al., Nature Comms. 12, 2272 (2021)

Speaker: Andrew Goodwin (norganic Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, UK)

24 Application of pair distribution function for study of highly-disoredred compounds

Compared with crystalline counterparts, metallic glasses (MGs) have some superior properties, such as high yield strength, hardness, large elastic limit, high fracture toughness and corrosion resistance, and hence are considered as promising engineering materials. Fe- and Co-based amorphous alloys have been the subject of considerable research interest and activities for the last decades due to applications related to their outstanding soft magnetic properties. Structurally, metallic glasses can be classified as disordered materials. X-ray diffraction (XRD) using high-energy photons has proven to be well suited for describing the structure of highly disordered systems such as MGs. Time-resolved in situ XRD experiments may nowadays be performed at high-brilliance synchrotron radiation sources for a variety of conditions which help to elucidate the structure–property relations.

In this contribution structural changes occurring in an Fe72.5Cu1Nb2Mo2Si15.5B7 alloy during a combination of constant rate heating (20 K/min) and isothermal holding at 500 and 520 C will be investigated using in situ high-energy X-ray diffraction. It was found that the ferromagnetic-to-paramagnetic transition of the amorphous phase is revealed as a change in the slope of the thermal expansion curve when heating a sample at a constant rate up to 520 C. Real space analysis by means of the atomic pair distribution function (PDF) demonstrated that the rate and extent of the thermal expansion strongly depend on the interatomic separation. The PDF proved to be a reliable method for the description of crystallization kinetics. Further it allows determination of sizes of ultrafine nanocrystals with grain sizes well below 8 nm and thus makes observation of early stages of nanocrystallization possible. This contribution presents results showing how pair distribution function can be successfully used for tracking the ferromagnetic-to-paramagnetic transition of amorphous phase in the vicinity of the Curie point.

Speaker: Jozef Bednarčík (P.J. Safarik University in Kosice, Faculty of Science, Institute of Physics, Slovakia)

25 Effect of Local Structure on Cation Insertion into Transition-Metal Oxides for Rechargeable Batteries with High Safety

Toward the realization of a low-carbon society through the effective use of renewable energy, lithium-ion rechargeable batteries (LIBs) are being applied not only to portable devices but also to electric vehicles. This situation makes it to be an urgent business to develop new electrode materials with higher safety as well as higher discharge capacity than commercially available LIBs electrodes. For example, Wadsley-Roth Ti-Nb-O materials such as TiNb₂O₇ have attracted much attention as candidates for new negative-electrode materials (anode materials) in the last decade. In the crystal structure of TiNb₂O₇, Ti and Nb occupy the same crystallographic sites, and lithium ions can be inserted into interstitial space in the network formed by MO₆ octahedra (M = Ti and Nb). However, the distribution of Ti and Nb in the crystal remains unknown. Moreover, the amorphization caused by the ball-milling process used to produce fine powder during electrode fabrication deteriorates the negative-electrode properties, and thus it is expected to elucidate the change in atomic configuration by the ball milling. Against this background, we investigated the atomic configuration of TiNb₂O₇ by X-ray and neutron total scattering measurements.
In the reduced pair distribution functions G(r), no change was observed in the short range up to 3.3 Å after the ball-milling treatment. On the other hand, in the intermediate range above 3.5 Å, the structural disorder caused by the treatment was remarkable. These results indicate that the ball milling disturbs the network structure while maintaining MO₆ octahedra, and such disordering is considered to prevent the Li insertion.

Speaker: Naoto Kitamura (Tokyo University of Science)

10:40 Coffee break

Fr2

26 Order within disorder in oxide glasses and liquids

The advent of quantum beam sources, which can generate high-flux high-energy X-rays/neutrons, and the development of advanced instrumentations make it feasible to probe atomic arrangement in disordered materials at atomistic level with a high real space resolution. A combination of quantum-beam diffraction and data-driven structural modeling such as reverse Monte Carlo enables us to study topological order in disordered materials. We introduce recent research topics on probing the topological order in oxide glasses and liquids revealed by several topological analyses (ring size, cavity volume, and homology) on the atomistic configuration derived by combined molecular dynamics (MD)-RMC modeling based on X-ray and neutron diffraction data. Finally, we introduce extraordinarily-ordered glasses and liquids to discuss the relationship between diffraction peaks and intermediate-range order in disordered materials.

Speaker: Shinji Kohara (National Institute for Materials Science)

27 Structural characterization and reversible laser-assisted modification of chalcogenide photonic media

The super-bandgap laser irradiation of the in situ prepared As-S chalcogenide films was found to cause drastic structural transformations and unexpected selective diffusion processes, leading to As enrichment on the nanolayer surface. Excitation energy dependent synchrotron radiation photoelectron spectroscopy showed complete reversibility of the molecular transformations and selective laser-driven mass transport during "laser irradiation"-"thermal annealing" cycles. Molecular modeling and density functional theory calculations performed on As-rich cage-like nonoclusters built from basic As1S3, As2S2 and As3S1 structural units indicate that the underlying microscopic mechanism of laser induced transformations is connected with the realgar-pararealgar transition in the As-S structure. The detected changes in surface composition as well as the related local and molecular structural transformations are analyzed and a model is proposed and discussed in detail. It is suggested that the formation of a concentration gradient is a result of bond cleavage and molecular reorientation during transformations and anisotropic molecular diffusion.

Speaker: Roman Holomb (Wigner Research Centre for Physics, Hungary)

28 Lithium ion transport environment by molecular vibrations in ion-conducting glasses

Controlling Li ion transport in glasses at atomic and molecular levels is key to realising all-solid-state batteries, a promising technology for electric vehicles. In this context, Li3PS4 glass, a promising solid electrolyte candidate, exhibits dynamic coupling between the Li+ cation mobility and the PS43− anion libration, which is commonly referred to as the paddlewheel effect1. In addition, it exhibits a concerted cation diffusion effect (i.e., a cation–cation interaction), which is regarded as the essence of high Li ion transport. However, the correlation between the Li+ ions within the glass structure can only be vaguely determined, due to the limited experimental information that can be obtained. We report that the Li ions present in glasses can be classified by evaluating their valence oscillations via Bader analysis to topologically analyse the chemical bonds. We found that three types of Li ions are present in Li3PS4 glass, and that the more mobile Li ions (i.e., the Li3-type ions, see Figure) exhibit a characteristic correlation at relatively long distances of 4.0–5.0 Å. Furthermore, reverse Monte Carlo simulations combined with deep learning potentials that reproduce X-ray, neutron, and electron diffraction pair distribution functions showed an increase in the number of Li3-type ions for partially crystallised glass structures with improved Li ion transport properties2. Our results show order within the disorder of the Li ion distribution in the glass by a topological analysis of their valences.

Keywords: sulfide glass, solid electrolyte, valence oscillation, pair distribution function

Speaker: Koji Ohara (Shimane University)

12:40 Lunch

Fr3

29 Constrained big-box modelling of Prussian blue analogues

Constrained big-box modelling of Prussian blue analogues

$^1$*E. A. Harbourne, $^1$J. Cattermull, $^1$N. Roth, $^2$David A. Keen, $^1$A. L. Goodwin

$^1$Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, United Kingdom
$^2$ISIS Facility, Rutherford Appleton Laboratory, Harwell Campus, Didcot, OX11 0QX

$^1$elodie.harbourne@hertford.ox.ac.uk, University of Oxford, United Kingdom

Prussian blue analogues (PBAs) are a compositionally diverse family of materials with applications as potassium-ion cathodes 1, heterogeneous catalysts [2], and gas-storage media [3,4]. Their structures are based on a simple cubic network of cyanide-linked transition metals. Despite this simplicity, they harbour a wide variety of different distortions and defect structures [5]. We have a longstanding interest in seeking to understand the nature of these defect structures and their implications for materials properties.

This contribution will describe a recently-developed Monte Carlo-driven big-box modelling approach, which we are using to develop atomistic representations of the canonical PBA system Mn[Pt(CN)6] by refining against X-ray pair distribution function measurements and conventional X-ray Bragg diffraction patterns. Our implementation makes use of the TOPAS refinement software [6] and aims to minimise the number of structural degrees of freedom used during model development.

1 S. Dhir, S. Wheeler, I. Capone, M. Pasta, Chem, 6, 2442 (2020).
[2] C. Marquez, F. G. Cirujano, C. V. Goethem, I. Vankelecom, D. D. Vos, T. D. Baerdemaeker, Catal. Sci. Technol. 8, 2061 (2018).
[3] S. S. Kaye, J. R. Long, J. Am. Chem. Soc. 127, 6506 (2005).
[4] L. Hu, P. Zhang, Q. W. Chen, N. Yan, J. Y. Mei, Dalton Trans. 40, 5557 (2011).
[5] J. Cattermull, M. Pasta, A. L. Goodwin, Mater. Horiz. 8, 3178 (2021).
[6] A. A. Coelho, TOPAS-Academic, version 6 (computer software); Coelho Software: Brisbane, 2016.

Speaker: Ms Elodie Harbourne (Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, UK)

30 Structure of Lithium Tellurite and Vanadium Lithium Tellurite Glasses by High Energy X-ray and Neutron Diffraction

The mixed ionic and electronic conduction in glasses has the potential to be used as a cathode in Li-ion batteries. The yLi2O-(100-y)TeO2 and xV2O5-(25-x)Li2O-(100-x-y)TeO2 glasses, (where x= 1,2,3,4, and 5 mol% and y= 20 and 25 mol%) were prepared by melt quenching, and their thermal, vibrational, and structural parameters are being calculated by differential scanning colorimetry, Raman spectroscopy, high-energy X-ray and neutron diffraction, and Reverse Monte Carlo (RMC) simulations. It was found that the glass transition temperature increased steadily with varying contents of 1–5 mol% of V2O5 in the lithium tellurite glass network due to an enhancement in the average single bond enthalpy. The combined datasets of X-ray and neutron diffraction were modelled by the RMC technique, and the Te-O, V-O, Li-O, and O-O distributions show their first peaks in the range of: 1.85–1.90 Å, 1.75–1.95 Å, 1.85-2.15 Å, and 2.70–2.80 Å, respectively. The average Te-O coordination number decreases with an increase in Li2O mol% in lithium tellurite glasses, whereas the V-O coordination number significantly decreases from 5.12 to 3.81 with an addition of V2O5 mol% in lithium tellurite glasses. The bond angle distribution of O-Te-O, O-V-O, O-Li-O, and O-O-O linkages has maxima in the following ranges: 86o-89o, 82o-87o, 80o-85o, and 59o, respectively. Moreover, the glass network also revealed the wide range of existence of Te-O and Te-Te distance over short- and medium-range disorders in the first coordination shell.

References:
[1] Alderman, O. L., Benmore, C. J., Feller, S., Kamitsos, E. I., Simandiras, E., Liakos, D.G.,Jesuit, M., Boyd, M.,Packard, M. & Weber, R. (2019). The Journal of Physical Chemistry Letters 11, 427-431.
[2] Dimitriev, Y. & Dimitrov, V. (1978). Materials Research Bulletin 13, 1071-1075.
[3] Hoppe, U., Yousef, E., Rüssel, C., Neuefeind, J. & Hannon, A. (2002). Solid State Communications 123, 273-278.
[4] Fabian, M., Jovari, P., Svab, E., Mészáros, G., Proffen, T. & Veress, E. (2007). Journal of Physics: Condensed Matter 19, 335209.
[5] Kaur, A., Khanna, A., Fábián, M., Krishna, P. & Shinde, A. (2019). Materials Research Bulletin 110, 239-246.

Speaker: Dr Hirdesh Hirdesh (Centre For Energy Research , Hungary, Budapest)

31 Structure determination of highly concentrated aqueous electrolyte solutions applying several interatomic potential models and RMC_POT simulations

Despite years and efforts, determining the structure of highly concentrated aqueous solutions is still a challenge. The complete description of the structure of a 4-component system (anion, cation, water oxygen, water hydrogen) at the two-particle correlation level would require the combination of ten independent experimental data sets. However, the number of available data sets is significantly lower. The low partial weights of the ion-related partials in the measured data (especially in dilute solutions) can be another problem.
Several solutions have been investigated previously in our group. Initially, attempts were made to determine the structure by fitting only diffraction data with RMC. Due to the lack of information, the shape of several partial radial distribution functions (PRDFs) was not well defined. Later, PRDFs calculated from MD simulations were added to the data sets to be fitted. This technique contributes highly to the determination of the structure, but the appropriateness of the interaction potential (force field, FF) used fundamentally determines the validity of the results obtained.
This problem can be solved by examining and combining several FFs. By comparing the models, a better description of the structure can be obtained even if no FF has been found that reproduces the structural functions from diffraction measurements with sufficient accuracy.
By further refining the model configurations with RMC_POT simulations, particle configurations can be obtained that are compatible with the diffraction data, while their potential energy is minimal and their structure is as close as possible to that obtained from MD simulations.
In this presentation, the structure determination technique based on the application of many FFs will be presented by investigating LiCl, CsCl, and CsF solutions.

Speaker: Ildikó Pethes

15:30 Coffee break

Fr4

32 FracfitSAXS linear programming, pair density distribution beyond Dmax

Small Angle Scattering (SAS) plays a central role in deciphering bimolecular shapes and structures. Central to its application is the specification of a Dmax, an intrinsically artificial parameter that defines the width of the pair-density distribution. The fracfitSAXS approach presents an alternative transformative method that recasts the analysis of scattering phenomena. In a departure from conventional SAS fitting strategies, the approach ingeniously reformulates the problem into a linear programming problem (LPP), opening up new perspectives.

In practice, this approach is used to decipher the intricate architecture of the low-density lipoprotein (LDL) core embedded in a membrane, an area of great importance in the context of cholesterol metabolism. Cleverly linking in situ SAS data with ex-situ cryo-electron microscopy (cryoEM) data provides a previously missing tool. This synergy improves our understanding of the intricate LDL structure and its dynamic interplay with apolipoprotein B-100 (apo B-100).

Another successful application involves the global energy demand and the need for the Green Deal initiative. In this context, the search for sustainable alternatives is gaining importance. The enzyme cellobiose dehydrogenase (CDH) is a compelling candidate due to its central role in lignocellulosic biomass utilization. Research into the mechanisms of the two-domain system of CDH and its transition between open and closed configuration, a crucial aspect of the regulation of electron transfer, is coming to the fore. With the presented approach, it can be shown that these dynamics are mainly controlled by electrostatic interactions, underlining the potential of CDH in the development of sustainable materials.

Speaker: Rupert Tscheliessnig

33 Structural features deduced from X-ray diffraction and persistent homology analysis of monatomic metallic liquids

In recent years, machine learning using liquid metal properties and theoretical models as input has led to rapid progress in the development of metallic glasses as well as many functional materials. It is therefore expected to become important in the future to use liquid structures as training data for machine learning to predict glass-forming ability. However, as metallic glasses are often multicomponent alloys, it takes a lot of time to cover their liquid structures. Therefore, it is important to predict the liquid structure of alloys from monatomic liquid structures, but at present, the accurate liquid structure data of some elements with particularly high melting points are not available. Therefore, the aim of this study was to systematise liquid structure information by focusing on the main constituent elements of metallic glasses and performing precise structure analysis of metallic liquids at high temperature typically over 2000 K. In the present study, structural data for eight elements, including Hf with a melting point of 2506 K, were measured using a combination of synchrotron X-ray diffraction and aerodynamic levitation at SPring-8. Persistent homology analysis was performed on 3D coordinates obtained from RMC modelling performed on the S(Q), and relationships with physical properties such as molar volume and entropy were investigated.

Speaker: Akitoshi Mizuno ((1) National Institute of Technology, Hakodate College, (2) National Institute for Materials Science)

34 Is there something really new in the field of materials analysis? Spoiler: yes, there is

Laboratory X-ray source based high-energy-resolution spectrometers have been showing a renaissance that culminated in radical progression recently. Although techniques like X-ray Absorption Near Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS) or X-ray Emission Spectroscopy (XES) were pioneered mainly on laboratory scale instruments, they have matured dramatically with the advent of synchrotron X-ray sources. The obvious excellence of these large scale photon sources in terms of X-ray brilliance, energy tunability, polarization, pulsed time structure, etc. over the conventional X-ray tubes turned the techniques mentioned dependent almost exclusively on occasionally accessible synchrotron beamtimes. However, the emergence of modern laboratory X-ray tube based spectrometers in the recent decade is being widely recognised, which give rise to a clear demand for such instruments.
Here, an overview will be given on the present status of lab-based high-energy-resolution X-ray spectrometers with selected use cases.

[1] Z. Németh, J. Szlachetko, É.G. Bajnóczi, G. Vankó, Rev. Sci. Instrum. 87(10), 2016, 103105.
[2] É.G. Bajnóczi, Z. Németh, G. Vankó, Inorg. Chem. 56(22), 2017, 14220.
[3] Z. Németh, É.G. Bajnóczi, Cs Bogdan, G. Vankó, PhysChemChemPhys 21(18), 2019, 9239.
[4] Z. Németh, A. Mikeházi, G. Vankó, J. Synch. Rad. 29, 2022, 1216.

Speaker: Z Nemeth

Saturday, 23 September

Sa1

35 Exploring local atomic structure in multicomponent materials with X-ray absorption spectroscopy and reverse Monte Carlo simulations

X-ray absorption spectroscopy (XAS) is an element-selective structural technique that provides information about the local environment of a specific element. In multicomponent materials, such as complex solid solutions, medium- and high-entropy alloys, XAS enables independent probing of each element by selecting the X-ray photon energy corresponding to its absorption edge. Consequently, a structural model of the material can be determined that agrees with all available experimental data, while considering static and thermal disorder, including correlation effects in atom motion. Solving this problem is challenging and requires the use of advanced methods based on atomistic simulations. This report will present and illustrate the approach based on reverse Monte Carlo simulations, with examples focusing on tungstates [1,2] and metal alloys [3].

[1] I.Pudza, A. Anspoks, G. Aquilanti, A. Kuzmin, Mater. Res. Bull. 153 (2022) 111910.
[2] G. Bakradze, E. Welter, A. Kuzmin, J. Phys. Chem. Solids 172 (2023) 111052.
[3] A.Smekhova, A. Kuzmin, K. Siemensmeyer, C. Luo, J. Taylor, S. Thakur, F. Radu, E. Weschke, A. Guilherme Buzanich, B. Xiao, A. Savan, K. V. Yusenko, A. Ludwig, Nano Res. 16 (2023) 5626-5639.

Speaker: Alexei Kuzmin (Institute of Solid State Physics, University of Latvia, Riga, Latvia)

36 Molecular RMC on Amorphous [(PhSn)4S6]

In recent years [(PhSn)4S6] and other similar molecular amorphous materials have gathered some interest due to their ability to convert a low power infrared laser beam into a continuous spectrum in the visible region while maintaining the low divergence and direction of the incoming beam.[1] To explore the structural background of this effect a hybrid move molecular RMC approach was used.[2]

[1] N.W. Rosemann, J.P. Eussner, A. Beyer, S.W. Koch, K. Volz, S. Dehnen, S. Chatterjee, Science 2016, 352, 1301–4.
[2] B.D. Klee, B. Paulus, J. Link Vasco, S. Hosokawa, J.R. Stellhorn, S. Hayakawa, S. Dehnen, W.-C. Pilgrim, Scripta Materialia 2022, 219, 114851.

Speaker: Benjamin Klee

37 The influence of lattice anisotropy on the local dynamics in hexagonal titanium and zirconium metals

Thorough examination of the lattice dynamics of hexagonal close-packed titanium and zirconium was conducted in this study using the extended X-ray absorption fine structure (EXAFS) spectroscopy. The analysis of Ti and Zr K-edge EXAFS spectra, employing the reverse Monte Carlo method [1], facilitated the determination of mean-squared relative displacements (MSRDs) for Ti-Ti and Zr-Zr atom pairs. By comparing these MSRDs with the literature data from [2], the study revealed their dependence on temperature and interatomic distances. Furthermore, it observed and compared the influence of hexagonal lattice anisotropy on the local dynamics in both metals.
[1] J. Timoshenko, A. Kuzmin, J. Purans, J. Phys.: Condens. Matter 26 (2014) 055401.
[2] L.-M. Peng, G. Ren, S. L. Dudarev, M. J. Whelan, Acta Cryst. A 52 (1996) 456-470.

Speaker: Vitalijs Dimitrijevs (Institute of Solid State Physics University of Latvia, EXAFS spectroscopy laboratory)

10:40 Coffee break

Sa2

38 A generalized scheme for characterizing orientational correlations in condensed phases of high symmetry molecules: SF₆ and C₆₀

The orientational correlation scheme introduced earlier for tetrahedral molecules [R. Rey, J. Chem. Phys., 126 (2007) 164506] is extended [L. Temleitner, J. Mol. Liq., 341 (2021) 116916.] for being able to classify orientational correlations between pairs of high symmetry molecules. While in the original algorithm a given orientation of a pair of tetrahedral molecules is characterized unambiguously by the number of ligand atoms that can be found between two planes that contain each centre and are perpendicular to the centre-centre connecting line, in the generalized algorithm, the planes are replaced by cones, whose apex angles are set according to the symmetry of each molecule. The applicability of the method is demonstrated in the room temperature crystalline structure of the C₆₀ molecules (representing the icosahedral symmetry) and the octahedral-shaped SF₆ molecule in a wide range of phases (gaseous, supercritical fluid, liquid and plastic crystalline) using classical molecular dynamics. Among the available forcefields, the most suitable chosen by reproducing earlier measured diffraction patterns and experimental densities.

Speaker: Laszlo Temleitner (Wigner Research Centre for Physics)

39 Probing NiO lattice dynamics by X-ray absorbtion spectroscopy combined with reverse Monte Carlo method

Lattice dynamics of bulk NiO was studied at seven temperatures from 10 K to 300 K using the Ni K-edge X-ray absorption spectroscopy combined with the reverse Monte Carlo simulations. Lattice dynamics calculations with empirical potential were also performed for comparison. The potential model was validated by comparing the experimental Ni K-edge extended X-ray absorption fine structure (EXAFS) spectrum of NiO with the results of molecular dynamics simulations at 300 K.
As a result of both calculation methods, the mean-square relative displacements (MSRDs) for Ni-O and Ni-Ni atom pairs were determined, showing their temperature and interatomic distance dependencies. An unexpected increase in the MSRD values for O atoms in the 3rd coordination shell of nickel was observed.

Speaker: Julija Lukasevica (Institute of Solid State Physics, University of Latvia, Latvia)

40 Machine learning assisted reverse Monte Carlo modeling for neutron total scattering data

In the area of atomic-level structure modeling, there are two well known parallel problems. The theory driven modeling usually cannot fully account for the disorder of practical system and therefore may fail to reproduce the complete picture of structure model as observed experimentally. The data driven approach tries to derive the structural model from the experimental data in a reverse manner (i.e., data to model) and therefore naturally is able to catch features observed experimentally. But quite often it lacks the accurate coverage of energetic landscape from the theoretical perspective. In this contribution, we aim at bringing in a novel approach combining the theoretical and experimental considerations. To realize this, the LAMMPS module for energy calculation is implemented into the reverse Monte Carlo routine (here, the RMCProfile package was used) for modeling total scattering data. Through such a combined approach, atomic positions would be adjusted according to the agreement with experimental scattering data and the energy landscape simultaneously. Specifically concerning the energy calculation, the Gaussian processing based machine learning routine for potential field construction is employed here. Such an approach, at the same time providing density functional theory level of accuracy, guarantees a reasonably short computational time which is required for the metropolis algorithm for structure modeling. The LAMMPS implemented RMCProfile package for conducting the combined modeling is generally applicable to utilize neutron and X-ray total scattering data, X-ray absorption spectroscopy data, electron scattering data, etc. for structure modeling to provide insights into structure-property link of general condensed matter systems.

Speaker: Yuanpeng Zhang (ORNL)

41 Closing

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Speaker: Laszlo Pusztai (Wigner RCP)

12:40 Lunch