paper

Ab-initio procedure for effective models of correlated materials with entangled band structure

arXiv:0906.1344 · doi:10.1103/PhysRevB.80.155134

Abstract

We present a first-principles method for deriving effective low-energy models of electrons in solids having entangled band structure. The procedure starts with dividing the Hilbert space into two subspaces, the low-energy part (" space'') and the rest of the space (" space''). The low-energy model is constructed for the space by eliminating the degrees of freedom of the space. The thus derived model contains the strength of electron correlation expressed by a partially screened Coulomb interaction, calculated in the constrained random-phase-approximation (cRPA) where screening channels within the space, , are subtracted. One conceptual problem of this established downfolding method is that for entangled bands it is not clear how to cut out the space and how to distinguish from the total polarization. Here, we propose a simple procedure to overcome this difficulty. In our scheme, the subspace is cut out from the Hilbert space of the Kohn Sham eigenfunctions with the help of a procedure to construct a localized Wannier basis. The subspace is constructed as the complementary space orthogonal to the subspace. After this disentanglement, becomes well defined. Using the disentangled bands, the effective parameters are uniquely determined in the cRPA. The method is successfully applied to 3 transition metals.

14 pages, 4 figures

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