First-principles calculation of x-ray absorption-edge structure in molecular clusters

We report initial results of a systematic study of the calculation of near-edge features in the x-ray absorption spectra of an atom in a molecular cluster as a function of different chemical environments and of varying prescriptions for the effective molecular potential of the excited electron. For a test-case comparison of the $K$ edges of Ge${\mathrm{Cl}}_4$ and Ge${\mathrm{H}}_4$, we find that the chemically induced changes in the molecular potential lead to large changes in the occurrence and strengths of bound-state and shape-resonance spectral features, in semiquantitative agreement with observation.