Relative stability, electronic structure, and magnetism of MnSe in rocksalt and zinc-blende structures

The structural, electronic, and magnetic properties of MnSe in the rocksalt (RS) and zine-blende (ZB) structures with various magnetic arrangements are investigated using spin-polarized density functional theory, with both generalized gradient approximation (GGA) and GGA+U method including an on-site Coulomb repulsion U to exchange and correlation. It is found that with GGA the ground-state of MnSe in the RS structure is an antiferromagnetic insulator with type-II spin ordering (AF2) and for the ZB polymorph it is an AF3 insulator, both consistent with experiments. However, GGA predicts that the ZB polymorph is more stable than the RS structure, which is in contradiction to observed facts, and the use of GGA+U method with U up to 8 eV still fails to overcome this deficiency. Furthermore, the calculated total energies are used to fit the magnetic exchange coupling constants in terms of a classical Heisenberg Hamiltonian, and Hubbard U of about 4 eV is necessary to obtain coupling constants as well as the magnetic phase transition temperatures in agreement with experiments.