COMPARISON OF THEORETICAL METHODS FOR THE CALCULATION OF EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE

Single-scattering calculations of extended x-ray-absorption fine-struc ture (EXAFS) amplitude and phase were compared with the experimental f irst-shell data for copper, rhodium, and platinum metal. Theoretical s tandards used were the tables of Teo and Lee, the tables of McKale et al., and the codes EXCURV90, MUFPOT, and FEFF. The quality of the expe rimental data was shown to be very high. The experimental first-shell data were obtained by Fourier filtering. The errors introduced in the separation of the first shell from the complete EXAFS spectrum by Four ier filtering were negligible as shown in a model study. The compariso n of experimental and theoretical data shows that the accuracy of theo retical standards depends mainly on the treatment of the exchange pote ntial and the energy-dependent losses. The most accurate description o f the exchange potential is the energy-dependent Hedin-Lundqvist poten tial with an energy-dependent self-energy, as used in FEFF. The use of ground state X alpha or energy-independent exchange, as in the tables of McKale et al. or the codes EXCURV90 and MUFPOT, is found to be ina dequate and leads to large phase and amplitude errors. Addition of an energy-dependent mean free path to the tables of McKale et al. improve d the accuracy by 15-25%. The physical reasons for the differences in accuracy of the theoretical methods examined are discussed.