Alternative approach to separable first-principles pseudopotentials

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Abstract
We construct a first-principles pseudo-Hamiltonian using ideas borrowed from the linear augmented-plane-wave method. Space is subdivided into the core region around the nuclei and the valence region, which is just the remainder of space. A basis set consisting of atomic-type orbitals in the core region and plane waves in the valence region leads to Hamiltonian and overlap matrices that depend on the plane-wave expansion coefficients only. The Hamiltonian and overlap matrices have the extremely useful property that their nonlocal part is separable. This allows eigenvectors and eigenvalues to be calculated with O(n ln(n)) operations, where n is the number of plane waves. The method is also well suited for first-row atoms. As an example we present results obtained for oxygen.