Anharmonic correlated Einstein model in XAFS theory and application

XAFS method is currently developed in both theoretical and experiment. It requires models to construct theory as well as to explain the experimental results or deduce the physical parameters from experimental data. The current XAFS theory now is harmonic theory and has been used to calculate some thermodynamic parameters. The result coincides well with XAFS spectrum measuring at low temperatures. But as temperature increases phonons interact with each other and lead to anharmonic effects resulting in various high-temperature universal XAFS for information on various structures. This study is aimed to provide theoretical basis of X-ray and XAFS spectrum and also participating in solving several important problems of modern XAFS theory when anharmonic effects or phonon interaction contribution are significant.