Soft-X-Ray Absorption Threshold in Metals, Semiconductors, and Alloys

We report calculations of the $K$ edges in Li and Be and the $L_{23}$ edges in Na, Mg, Al, and Si. The calculations use self-consistent core and valence-electron densities for both the ground and excited configurations; corrections for the host ionic fields are incorporated, using pseudopotential methods. It is found that the calculated edge energies are in close agreement with experiment when Schneider's values of the bulk chemical potential are used for the excited electron. In further studies of inhomogeneous systems, we show that the core threshold is highly insensitive to atomic environment, so that amorphous materials can be discussed. The case of dilute alloys is treated and core recombination in AlMg alloys is analyzed in detail. The effects studied here indicate that the surface barriers caused by the dipole moments of surface atoms are small, most probably $\lesssim 0.1$ Ry, in all the materials treated here.