An ab initio LAPW study of the α and β phases of bulk molybdenum trioxide, MoO3

Structure and electronic properties of the α and β-MoO3, have been studied with periodic LAPW calculations. The structure and electronic properties of the α-MoO3 are in quite agreement with experimental and previous theoretical results. The oxide is partially ionic and the symmetrically bridging oxygens exhibit more ionic feature while the terminal oxygens are more covalent. The lattice scaling of the β-MoO3 give results in excellent agreement with the reported experimental pseudo-cubic results. It has been found from density of states (DOS) that β-MoO3 is not fully ionic system and some covalent contributions are still appreciable. These covalent contributions to the bonding appear derisory compared to the covalent contributions of the α phase. The β-MoO3 → α-MoO3 transformation is explained by metal off-center displacement toward O1 (and a little less toward O2) centers which is stabilized by an increase in covalency between the Mo and oxygen atoms.