Abstract
Ab initio calculations of the As K-edge XAFS of a-As2S3, encompassing both XANES and EXAFS, were performed using a curved-wave multiple-scattering (MS) approach applied to an atomic cluster representing the amorphous solid. The XAFS function obtained this way is combined with the calculated absorption cross section to simulate the experimental absorption spectrum. The experimental absorption edge structure is resolved into two components, one representing a bound excited state resonance and the second due to transitions to the continuum. The bound state resonance, represented by a Lorentzian, is located about 5.3 eV below the continuum threshold which in turn is simulated by an arctan function. The continuum structure is computed using χ and cross section data.