Embedded Peierls instability and the electronic structure of MoO2

Molybdenum dioxide crystallizes in a monoclinic structure which deviates on ly slightly from the rutile structure and is characteristic of several earl y 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 el ectronic properties of MoO2 are dominated by strong hybridization of O 2p a nd crystal-field-split Mo 4d states with bands near the Fermi energy origin ating almost exclusively from Mo 4d t(2g) orbitals. In additional calculati ons 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 m onoclinic structure, the characteristic metal-metal dimerization causes str ong splitting of the d(parallel to) bands into bonding and antibonding bran ches which embrace the nearly inert pi* bands at E-F. As a consequence, lar ge portions of the Fermi surface are removed. According to our calculations the monoclinic structure of MoO2 thus results from a Peierls-type instabil ity of the d(parallel to) bands in the presence of, but still rather unaffe cted by, an embedding background of pi* states. Our work has strong implica tions for the current understanding of VO2 and the striking metal-insulator /structural transition displayed by this material.