Reverse Monte Carlo modeling for low-dimensional systems

Reverse Monte Carlo (RMC) is one of the commonly used approaches for modeling total scattering data. However, to extend the capability of the RMC method for refining the structure of nanomaterials, the dimensionality and finite size need to be considered when calculating the pair distribution function (PDF). To achieve this, the simulation box must be set up to remove the periodic boundary condition in one, two or three of the dimensions. This then requires a correction to be applied for the difference in number density between the real system and the simulation box. In certain circumstances an analytical correction for the uncorrelated pairings of atoms is also applied. The validity and applicability of our methodology is demonstrated by applying the algorithms to simulate the PDF patterns of carbon systems with various dimensions, and also by using them to fit experimental data of CuO nanoparticles. This alternative approach for characterizing the local structure of nano-systems with the total scattering technique will be made available via the RMCProfile package. The theoretical formulation and detailed explanation of the analytical corrections for low-dimensional systems – 2D nanosheets, 1D nanowires and 0D nanoparticles – is also given.

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The atomic structure of a MgCo2O4 nanoparticle for a positive electrode of a Mg rechargeable battery

Chemical Communications ◽

10.1039/c8cc09713e ◽

2019 ◽

Vol 55 (17) ◽

pp. 2517-2520 ◽

Cited By ~ 6

Author(s):

Naoto Kitamura ◽

Yuhei Tanabe ◽

Naoya Ishida ◽

Yasushi Idemoto

Keyword(s):

Monte Carlo ◽

Atomic Structure ◽

Positive Electrode ◽

Scattering Data ◽

Rechargeable Battery ◽

Reverse Monte Carlo ◽

Spinel Type ◽

Total Scattering ◽

X Ray ◽

Neutron Total Scattering

The atomic structure of a spinel-type MgCo2O4 nanoparticle was investigated by the reverse Monte Carlo modelling using X-ray and neutron total scattering data.

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New capabilities for enhancement of RMCProfile: instrumental profiles with arbitrary peak shapes for structural refinements using the reverse Monte Carlo method

Journal of Applied Crystallography ◽

10.1107/s1600576720013254 ◽

2020 ◽

Vol 53 (6) ◽

pp. 1509-1518

Author(s):

Yuanpeng Zhang ◽

Maksim Eremenko ◽

Victor Krayzman ◽

Matthew G. Tucker ◽

Igor Levin

Keyword(s):

Monte Carlo ◽

Large Scale ◽

Bragg Diffraction ◽

Scattering Data ◽

Quality Data ◽

Reverse Monte Carlo ◽

Total Scattering ◽

Nanoscale Structures ◽

Oak Ridge ◽

Diffraction Patterns

Reported here are the development and application of new capabilities in the RMCProfile software for structural refinements using the reverse Monte Carlo (RMC) method. An algorithm has been implemented to enable the use of arbitrary peak-shape functions in the modeling of Bragg diffraction patterns and instrumental resolution effects on total-scattering data. This capability eliminates the dependence of RMCProfile on preset functions, which are inadequate for data produced by some total-scattering instruments, e.g. NOMAD at the Spallation Neutron Source (SNS) at Oak Ridge, Tennessee, USA. The recently developed procedure for the instrument-resolution correction has been modified to improve its accuracy, which is critical for recovering nanoscale structure. The ability to measure fine details of local and nanoscale structures with high fidelity is required because such features are increasingly exploited in the design of materials with enhanced functional properties. The new methodology has been tested via RMC refinements of large-scale atomic configurations (distances up to 8 nm) for SrTiO3 using neutron total-scattering data collected on the Polaris and NOMAD time-of-flight powder diffractometers at the ISIS facility (Didcot, Oxfordshire, UK) and SNS, respectively. While the Polaris instrument is known to provide the high-quality data needed for RMC analysis, the similar and sound atomic configurations obtained from both instruments confirmed that the NOMAD data are also suitable for RMC refinements over a broad distance range.

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Advancing reverse Monte Carlo structure refinements to the nanoscale

Journal of Applied Crystallography ◽

10.1107/s1600576717013140 ◽

2017 ◽

Vol 50 (6) ◽

pp. 1561-1570 ◽

Cited By ~ 11

Author(s):

M. Eremenko ◽

V. Krayzman ◽

A. Gagin ◽

I. Levin

Keyword(s):

Monte Carlo ◽

Scattering Data ◽

Full Potential ◽

Reverse Monte Carlo ◽

Computationally Efficient ◽

Total Scattering ◽

Correlation Lengths ◽

Atomic Displacements ◽

Current Limit ◽

The Fourier Transform

Over the past decade, theRMCProfilesoftware package has evolved into a powerful computational framework for atomistic structural refinements using a reverse Monte Carlo (RMC) algorithm and multiple types of experimental data. However, realizing the full potential of this method, which can provide a consistent description of atomic arrangements over several length scales, requires a computational speed much higher than that permitted by the current software. This problem has been addressedviasubstantial optimization and development ofRMCProfile, including the introduction of the new parallel-chains RMC algorithm. The computing speed of this software has been increased by nearly two orders of magnitude, as demonstrated using the refinements of a simulated structure with two distinct correlation lengths for the atomic displacements. The new developments provide a path for achieving even faster performance as more advanced computing hardware becomes available. This version ofRMCProfilepermits refinements of atomic configurations of the order of 500 000 atoms (compared to the current limit of 20 000), which sample interatomic distances up to 10 nm (versus3 nm currently). Accurate, computationally efficient corrections of the calculated X-ray and neutron total scattering data have been developed to account for the effects of instrumental resolution. These corrections are applied in both reciprocal and real spaces, thereby enabling RMC fitting of an atomic pair distribution function, which is obtained as the Fourier transform of the total-scattering intensity, over the entire nanoscale distance range accessible experimentally.

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Representational analysis of extended disorder in atomistic ensembles derived from total scattering data

Journal of Applied Crystallography ◽

10.1107/s1600576715016404 ◽

2015 ◽

Vol 48 (5) ◽

pp. 1560-1572 ◽

Cited By ~ 6

Author(s):

James R. Neilson ◽

Tyrel M. McQueen

Keyword(s):

Monte Carlo ◽

Tight Binding ◽

Basis Set ◽

Scattering Data ◽

Crystallographic Structure ◽

Reverse Monte Carlo ◽

Total Scattering ◽

Meaningful Information ◽

Order And Disorder ◽

Analysis Technique

With the increased availability of high-intensity time-of-flight neutron and synchrotron X-ray scattering sources that can access wide ranges of momentum transfer, the pair distribution function method has become a standard analysis technique for studying disorder of local coordination spheres and at intermediate atomic separations. In some cases, rational modeling of the total scattering data (Bragg and diffuse) becomes intractable with least-squares approaches, necessitating reverse Monte Carlo simulations using large atomistic ensembles. However, the extraction of meaningful information from the resulting atomistic ensembles is challenging, especially at intermediate length scales. Representational analysis is used here to describe the displacements of atoms in reverse Monte Carlo ensembles from an ideal crystallographic structure in an approach analogous to tight-binding methods. Rewriting the displacements in terms of a local basis that is descriptive of the ideal crystallographic symmetry provides a robust approach to characterizing medium-range order (and disorder) and symmetry breaking in complex and disordered crystalline materials. This method enables the extraction of statistically relevant displacement modes (orientation, amplitude and distribution) of the crystalline disorder and provides directly meaningful information in a locally symmetry-adapted basis set that is most descriptive of the crystal chemistry and physics.

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X-ray diffraction, neutron scattering and EXAFS spectroscopy of monoclinic zirconia: analysis by Rietveld refinement and reverse Monte Carlo simulations

Journal of Applied Crystallography ◽

10.1107/s0021889802006829 ◽

2002 ◽

Vol 35 (4) ◽

pp. 434-442 ◽

Cited By ~ 38

Author(s):

Markus Winterer ◽

Robert Delaplane ◽

Robert McGreevy

Keyword(s):

Monte Carlo ◽

Neutron Scattering ◽

Rietveld Refinement ◽

Local Structure ◽

Exafs Spectroscopy ◽

Scattering Data ◽

Accurate Information ◽

Reverse Monte Carlo ◽

Monoclinic Zirconia ◽

X Ray

Extended X-ray absorption fine structure (EXAFS) and neutron scattering data from monoclinic zirconia are analysed independently and simultaneously by reverse Monte Carlo (RMC) modelling. X-ray and neutron powder diffraction data are analysed by Rietveld refinement. The results are compared with respect to the local structure around the zirconium cations. Monoclinic zirconia was chosen as a model system for the comparison of structural information obtained by EXAFS spectroscopy and scattering methods because it is crystalline but also has some local disorder. In the case of zirconia, analysis of EXAFS spectra by RMC modelling results in reliable and accurate information on the local structure, consistent with neutron scattering and diffraction experiments.

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Short-Range Structure of Ti0.63V0.27Fe0.10D1.73 from Neutron Total Scattering and Reverse Monte Carlo Modelling

Energies ◽

10.3390/en13081947 ◽

2020 ◽

Vol 13 (8) ◽

pp. 1947

Author(s):

Henrik Mauroy ◽

Konstantin Klyukin ◽

Marina G. Shelyapina ◽

David A. Keen ◽

Annett Thøgersen ◽

...

Keyword(s):

Monte Carlo ◽

Hydrogen Storage ◽

Short Range ◽

Density Functional ◽

Metal Species ◽

Face Centered Cubic ◽

Reverse Monte Carlo ◽

Hydrogen Atoms ◽

Total Scattering ◽

Neutron Total Scattering

Ti-V-based body-centered cubic (BCC) alloys have potential for large-scale hydrogen storage if expensive vanadium is substituted with much cheaper Fe-containing ferrovanadium. Use of ferrovanadium reduces the alloys’ hydrogen storage capacity. This is puzzling since the amount of Fe is low and hydrogen atoms are accommodated in interstitial sites which are partly coordinated by Fe in many intermetallic compounds. The present work is aimed at finding a structural explanation for Fe-induced capacity loss in Ti-V alloys. Since such alloys and their hydrides are highly disordered without long-range occupational order of the different metal species, it was necessary to employ a technique which is sensitive to local structure. Neutron total scattering coupled with reverse Monte Carlo modelling was thus employed to elucidate short-range atomic correlations in Ti0.63V0.27Fe0.10D1.73 from the pair distribution function. It was found that Fe atoms form clusters and that the majority of the vacant interstitial sites are within these clusters. These clusters take the same face-centered cubic structure as the Ti-V matrix in the deuteride and thus they are not simply unreacted Fe which has a BCC structure. The presence of Fe clusters is confirmed by transmission electron microscopy. Density functional theory calculations indicate that the clustering is driven by thermodynamics.

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