Embedded Peierls instability and the electronic structure of MoO2

Molybdenum dioxide crystallizes in a monoclinic structure which deviates only slightly from the rutile structure and is characteristic of several early transition metal dioxides. We present results of all-electron electronic structure calculations based on density functional theory within the local density approximation and using the augmented spherical wave method. The electronic properties of MoO 2 are dominated by strong hybridization of O 2p and crystal-field-split Mo 4d states with bands near the Fermi energy originating almost exclusively from Mo 4d t 2g orbitals. In additional calculations for a hypothetical high-symmetry rutile structure these bands separate into quasi-one-dimensional d ∥ states pointing along the rutile c -axis and the rather isotropically dispersing π* bands. On going to the monoclinic structure, the characteristic metal-metal dimerization causes strong splitting of the d ∥ bands into bonding and antibonding branches which embrace the nearly inert π* bands at E F . As a consequence, large portions of the Fermi surface are removed. According to our calculations the monoclinic structure of MoO 2 thus results from a Peierls-type instability of the d ∥ bands in the presence of, but still rather unaffected by, an embedding background of π* states. Our work has strong implications for the current understanding of VO 2 and the striking metal-insulator/structural transition displayed by this material.