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 [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 -Fe 2O 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.
| Original language | English |
|---|---|
| Article number | 074105 |
| Journal | Journal of Chemical Physics |
| Volume | 136 |
| Issue number | 7 |
| DOIs | |
| State | Published - Feb 21 2012 |
Funding
K. Németh gratefully acknowledges helpful discussions with V. Krayzman (NIST, MD), I. Levin (NIST, MD), L. Pusztai (HAS-RISPO, Hungary), M. Tucker (ISIS, UK), and T. Proffen (LANL, NM). V. Weber (IBM, Switzerland) is acknowledged for computations-related assistance. The authors thank NERSC (U.S. DOE DE-AC02-05CH11231) for the use of computational resources. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357.