Efficient computational method for interstitial Green functions

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Abstract
A computational scheme is developed for the numerical evaluation of Green functions expanded around interstitial positions. The Green function matrix elements, consisting of a Brillouin zone and a Fermi surface integral, are calculated at one energy. The explicit occurrence of free-electron singularities in the integrand of the Brillouin zone integral complicates the evaluation and requires special computational effort. It is shown how, within the framework of the tetrahedron method, the problem of singular integrands can be resolved efficiently and adequately. A comparison with other evaluation schemes, based on a Kramers-Kronig relation or an approximate angular momentum expansion, is made. Special attention is given to the octahedral position in a FCC lattice.