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 MoO2 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(parallel to) states pointing along the rutile c-axis and the rather isotropically dispersing pi* bands. On going to the monoclinic structure, the characteristic metal-metal dimerization causes strong splitting of the d(parallel to) bands into bonding and antibonding branches which embrace the nearly inert pi* bands at E-F. As a consequence, large portions of the Fermi surface are removed. According to our calculations the monoclinic structure of MoO2 thus results from a Peierls-type instability of the d(parallel to) bands in the presence of, but still rather unaffected by, an embedding background of pi* states. Our work has strong implications for the current understanding of VO2 and the striking metal-insulator/structural transition displayed by this material.