Wannier-like functions and tight-binding parametrization for the manganese bands in CaMnO₃

Abstract

We study the electronic band structure of CaMnO₃, in order to understand the origin of the dispersion of the Mn(e_g) bands, which is in contrast with the predicted dispersionless bands within the Anderson-Hasegawa double-exchange model with infinite Hund's-rule coupling. A downfolding technique within the newly developed muffin-tin orbital-based method is used to analyse the density-functional band structure obtained in the local spin density approximation. The finite Hund's coupling parameter in realistic situations allows the same-spin bands on the two manganese sublattices to mix producing a large dispersion. The calculated Wannier functions for the Mn(e_g) bands also show large oxygen character at sites further away from nearest oxygen sites causing long-ranged Mn-Mn hopping processes.