Advanced classical anharmonic correlated Einstein model high-order expanded Debye-Waller factors and EXAFS

Abstract

The advanced classical anharmonic correlated Einstein model (ACACEM) is derived for the high-order expanded Debye-Waller factors (DWF) presented in terms of a cumulant expansion and extended X-ray absorption fine structure (EXAFS). The ACACEM advances the classical single-bond model first by including the many-body effects in DWF and EXAFS based on involving the interactions of absorber and backscatter atoms with their nearest neighbors, and secondly by correcting the absence of zero-point vibrations due to classical theory based on a created method providing all considered quantities using only the second cumulant or mean square relative displacement. The Morse potential is assumed to describe the single-pair atomic interaction included in the derived anharmonic effective potential. The ACACEM has developed into a semi-classical model involving the advantages of both classical and quantum theories. Numerical results for all considered quantities of Cu agree well with experiment.