PERTURBATION APPROACH TO THERMAL FACTORS IN EXAFS

Each of the cumulants is written in terms of lower order moments which are systematically calculated by use of temperature Green's functions and Wick's theorem. As an alternative approach, we present real space representation, which can be closely related to path integral represe ntation, and compared with classical expression widely used by several authors. We discuss the applicability and the limitation of the class ical integral expressions based on this quantum formula.