Efficient simultaneous reverse Monte Carlo modeling of pair-distribution functions and extended x-ray-absorption fine structure spectra of crystalline disordered materials

Károly Németh; Karena W Chapman; Mahalingam Balasubramanian; Badri Shyam; Peter J Chupas; Steve M Heald; Matt Newville; Robert J Klingler; Randall E Winans; Jonathan D Almer; Giselle Sandi; George Srajer

doi:10.1063/1.3684547

Efficient simultaneous reverse Monte Carlo modeling of pair-distribution functions and extended x-ray-absorption fine structure spectra of crystalline disordered materials

J Chem Phys. 2012 Feb 21;136(7):074105. doi: 10.1063/1.3684547.

Authors

Károly Németh¹, Karena W Chapman, Mahalingam Balasubramanian, Badri Shyam, Peter J Chupas, Steve M Heald, Matt Newville, Robert J Klingler, Randall E Winans, Jonathan D Almer, Giselle Sandi, George Srajer

Affiliation

¹ Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA. Nemeth@ANL.Gov

PMID: 22360234
DOI: 10.1063/1.3684547

Abstract

An efficient implementation of simultaneous reverse Monte Carlo (RMC) modeling of pair distribution function (PDF) and EXAFS spectra is reported. This implementation is an extension of the technique established by Krayzman et al. [J. Appl. Cryst. 42, 867 (2009)] in the sense that it enables simultaneous real-space fitting of x-ray PDF with accurate treatment of Q-dependence of the scattering cross-sections and EXAFS with multiple photoelectron scattering included. The extension also allows for atom swaps during EXAFS fits thereby enabling modeling the effects of chemical disorder, such as migrating atoms and vacancies. Significant acceleration of EXAFS computation is achieved via discretization of effective path lengths and subsequent reduction of operation counts. The validity and accuracy of the approach is illustrated on small atomic clusters and on 5500-9000 atom models of bcc-Fe and α-Fe(2)O(3). The accuracy gains of combined simultaneous EXAFS and PDF fits are pointed out against PDF-only and EXAFS-only RMC fits. Our modeling approach may be widely used in PDF and EXAFS based investigations of disordered materials.