Electronic structure of MPX3 trichalcogenide monolayers in density functional theory: a case study with four compounds (M = Mn, Fe; X = S, Se)

Structural, electronic and magnetic properties of four transition metal tri-chalcogenide monolayers-MnPS3, MnPSe3, FePS3 and FePSe3-are studied using density functional theory. Lattice structures in good agreement with experiments are obtained. Electronic structure of the Mn compounds obtained using the PBE-GGA functional is in qualitative agreement with the experiments, apart from the well known band gap problem. However, PBE fails for the Fe compounds. They turn out to be metallic, while experimentally they are characterized to be semiconductors. Inclusion of a Hubbard U term produces semiconducting states for both FePS3 and FePSe3. We are able to produce the correct anti-ferromagnetic state for all the four compounds. This is significant because some previous calculations reported FePSe3 to be non-magnetic. We obtain new insights into the bonding in these compounds through analyses of Bader charges and electron localization function, that justifies use of U on the Fe atoms. Effects of strain and spin-orbit coupling on the electronic structure are also studied. These calculations can serve as benchmarks for future studies on these materials.