PATH-INTEGRAL EFFECTIVE-POTENTIAL METHOD APPLIED TO EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE CUMULANTS

The path-integral effective-potential (EP) method was applied to the c alculations of extended x-ray-absorption fine-structure (EXAFS) cumula nts. Temperature dependence of the EXAFS cumulants up to the third or fourth order for diatomic Br-2 and solid fee Kr and Ni were evaluated. In the case of solid Kr, the pair-potential approximation was employe d to describe van der Waals interactions, while for Ni metal the embed ded atom method (EAM) that accounts for many-body interactions in meta llic bonds was applied. Although the EAM calculation is usually perfor med based on classical statistics, quantum-mechanical corrections were found to be carried out in a straightforward manner by means of the E P technique. The evaluated EXAFS cumulants were compared to those obta ined experimentally and excellent agreement was achieved. The usefulne ss of the EP technique in the study of temperature-dependent EXAFS is discussed by comparing the other approach of the quantum-statistical p erturbation theory.