ENSURING THE CONSTANCY OF THE CHEMICAL-POTENTIAL WITHIN THE LOCAL-DENSITY APPROXIMATION FOR EXCHANGE AND CORRELATION - IMPLICATIONS FOR NEAR-EDGE X-RAY-ABSORPTION FINE-STRUCTURE

We investigate the correct implementation of the exchange-correlation potential for the excited core electron in near-edge x-ray-absorption fine structure (NEXAFS). We examine the effects on NEXAFS spectra of the ground-state Slater and excited-state Dirac-Hara exchange potentials and current implementations of the Hedin-Lundqvist exchange-correlation potential on the muffin-tin model. For a test case of gas-phase acetylene, we find good agreement with prior experimental spectra only with the Hedin-Lundqvist potential implemented on the local-density approximation with a Thomas-Fermi-like requirement of constancy of the chemical potential. © 1995 The American Physical Society.