Journal of Synchrotron Radiation

Volume 13, Part 4 (July 2006)

research papers

J. Synchrotron Rad. (2006). 13, 321-325 [ doi:10.1107/S0909049506018504 ]

Einstein and Debye models for EXAFS parallel and perpendicular mean-square relative displacements

M. Vaccari and P. Fornasini

Abstract: The correlated Einstein and Debye models for EXAFS parallel mean-square relative displacement (MSRD) are derived from the general expression in terms of eigenfrequencies and eigenvectors of the dynamical matrix, without ad hoc assumptions. The two models are generalized to parameterize also the EXAFS perpendicular MSRD. The physical meaning of Einstein frequencies, as well as the application of the Debye model to crystals with more than one atom per cell, are critically discussed.

Keywords: EXAFS; thermal disorder; mean-square relative displacements; Einstein model; Debye model.