Anharmonic effective potential, correlation effects, and EXAFS cumulants calculated from a Morse interaction potential for fcc metals

Anharmonic effective pair potentials and effective local force constants have been studied for fcc metals, assuming an interaction Morse potential and taking into account the influence of nearest neighbours of absorber and backscatterer atoms. Analytical expressions for the first three extended X-ray absorption fine structure (EXAFS) cumulants, as well as for the atomic mean square displacements, have been derived as a function of the Morse parameters. Numerical results for copper and nickel are compared with experimental data. A good agreement is found for the second cumulant. Non-negligible discrepancies are instead found for the first and third cumulants, which are tentatively attributed to the central nature of the Morse potential, which neglects many-body effects.