Structural and Magnetic Properties of MnTe Phases from Ab Initio Calculations

We present ab initio studies of NiAs, zinc-blende, wurtzite, and rocksalt MnTe with possible magnetic arrangements of Mn atoms using spin-polarized density functional theory and generalized gradient approximation for exchange and correlation. The impact of an empirical on-site Coulomb interaction U on the lattice constants and ground-state energies is especially studied for antiferromagnetic NiAs and zinc-blende phases, for which contradictory results are found. While U = 0 eV gives the correct energetic ordering of the crystal structures, the experimental lattice constants can only be reproduced for finite U = 2, ... ,4 eV. The Hubbard U also strongly influences the magnitude of the magnetic interaction parameters and hence the transition temperatures. In order to obtain Neel temperatures in agreement with experiment a value of about U = 4 eV is needed. We demonstrate how U affects the magnetic coupling via the localization of the Mn3d orbitals.