Electronic structure and lattice instability of metallic VO2

A first-principles energy-band study of the metallic rutile phase of VO2 using a general crystal potential and an expansion of the Bloch functions in a linear combination of atomic orbitals is reported. The results are compared with previous work and experimental optical, x-ray absorption and emission, and x-ray photoelectron spectroscopy data. We obtain a large density of states at the Fermi energy; the Fermi surface is found to be determined by the two lowest d bands, at the bottom of the "t2g" manifold which is split by the orthorhombic field; the lowest-band Fermi surface possesses some nesting features corresponding to a nesting vector q→=Γ R. A calculation of the generalized susceptibility in the constant-matrix-element approximation shows the existence of a maximum at the zone boundary R. We suggest that the formation of a charge-density wave with wave vector q→=Γ R accompanied by a periodic lattice distortion is thus possible; the subsequent condensation of phonons at the point R could then explain the crystallographic phase transition observed at T=339 K.