Parameter-free calculation of K alpha chemical shifts for Al, Si, and Ge oxides - art. no. 193102

The chemical shifts of the K alpha radiation line from Al, Si, and Ge ions between their elemental and oxide forms are calculated within the framework of density functional theory using ultrasoft pseudopotentials. It is demon strated that this theoretical approach yields quantitatively accurate resul ts fur the systems investigated, provided that relaxations of the valence e lectrons upon the core-hole transition are properly accounted for. Therefor e, such calculations provide a powerful tool for identification of impurity states based on x-ray fluorescence data. Results for an Al impurity implan ted in silica are found to be in excellent agreement with experimental data , providing support for the proposed atomic geometry.