Ab initio study of the x-ray edge in alkali metals and alloys

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An ab initio model is developed for calculating the approximate electronic structure of local excited states in alkali metals and alloys. Core excitations of Na and K metals are calculated along with core impurity excitations of K in Li and Rb in Li. Unrestricted Hartree-Fock method is used in conjunction with pseudopotentials, cluster theory, and Rayleigh-Schrödinger many-body perturbation theory to yield a spectroscopic accuracy of 0.1 eV when compared to experiment. Local resonance states below the interband threshold are found in the (n-1)p5s2 excited configurations in Na and K metals. Similar states are not found for the analogous excited configurations in dilute alloys of K in Li and Rb in Li. These results suggest that electron-hole pair interactions dominate the x-ray absorption process in pure alkali metals. Results are contrasted with current models for the enhancement of x-ray absorption. © 1989 The American Physical Society.

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Physical Review B