Atomic cluster-structure calculations of the X-ray near-edge absorption of silver

A development of the finite difference method is used to compute atomic-cluster absorption spectra. The spectra is compared with recent high-precision measurements of the X-ray mass absorption coefficient of silver in the X-ray absorption fine structure region. The comparison indicates that in the near-edge region the finite difference method reproduces the fine structure qualitatively. The dominant theoretical techniques currently used in the literature to model these systems are the muffin-tin approach, the discrete variational method, the full linear augmented plane-wave approach and the finite difference method for near-edge structure. This Letter concentrates on the finite difference method and finds that this can be extended to the dominant XAFS regime successfully. In most investigations, amplitudes and energy scaling allow apparently good agreement of theory to be obtained with experiment. However, on absolute scales this comparison becomes weaker. This Letter relates to experimental data measured on an absolute scale to high accuracy, and therefore reveals both considerable agreement but also particular areas of discrepancy. Remaining discrepancies between theory and experiment relating to edge height, relative peak amplitudes and widths are discussed and invite further study.