AB-INITIO XAFS CALCULATION FOR A-AS2S3

Ab initio calculations of the As K-edge XAFS of a-As2S3, encompassing both XANES and EXAFS, were performed using a curved-wave multiple-scat tering (MS) approach applied to an atomic cluster representing the amo rphous solid. The XAFS function obtained this way is combined with the calculated absorption cross section to simulate the experimental abso rption spectrum. The experimental absorption edge structure is resolve d into two components, one representing a bound excited state resonanc e 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 functi on. The continuum structure is computed using chi and cross section da ta.