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 calculations of extended x-ray-absorption fine-structure (EXAFS) cumulants. Temperature dependence of the EXAFS cumulants up to the third or fourth order for diatomic Br₂ and solid fcc Kr and Ni were evaluated. In the case of solid Kr, the pair-potential approximation was employed to describe van der Waals interactions, while for Ni metal the embedded atom method (EAM) that accounts for many-body interactions in metallic bonds was applied. Although the EAM calculation is usually performed based on classical statistics, quantum-mechanical corrections were found to be carried out in a straightforward manner by means of the EP technique. The evaluated EXAFS cumulants were compared to those obtained experimentally and excellent agreement was achieved. The usefulness of the EP technique in the study of temperature-dependent EXAFS is discussed by comparing the other approach of the quantum-statistical perturbation theory.