CORE-HOLE EFFECT ON THE XAS SI K-EDGE SHAPE IN ALPHA-QUARTZ

The role of the core hole effect on the Si K X-ray absorption spectrum of alpha-quartz is established thanks to two electronic structure cal culations: 1. a self-consistent band structure approach at ambient pre ssure and under hydrostatic pressure, that accounts for the gap and th e valence band shape, and that provides the empty density of states of alpha-quartz, is shown to be unable to reproduce the experimental Si K edge shape; 2. on the opposite, a self-consistent embedded cluster c alculation, which allows to include the effect of the core hole yields a local p density of states on an excited silicon atom which compares satisfactorily with the experimental spectrum.