Predicting EXAFS signals from shock compressed iron by use of molecular dynamics simulations

Simulated EXAFS signals from ab initio models and configurational averaging of molecular dynamics (MD) data are compared for alpha-Fe, and configurationally averaged MD EXAFS signals are compared with experimental data for iron shock compressed to pressures above the alpha-epsilon transition pressure. It is shown that molecular dynamics potentials and ab initio models capable of recreating similar vibrational density of states lead to EXAFS signals in good mutual agreement. The effects of the classical nature of the phonon distribution in the MD and the anharmonicity of the potential give rise to noticeable differences between ab initio models and configurational averaging of MD data. However, the greatest influence on the spectra is the form of the potential itself. We discuss the importance of these effects in simulating EXAFS spectra for shock compressed polycrystalline iron. It is shown that EXAFS is an insensitive probe for determining the nature of the close packed product phase in this system. (C) 2009 Elsevier B.V. All rights reserved.