ELECTRONIC-STRUCTURE CALCULATIONS FOR 2-DIMENSIONAL TRANSITION-METAL OXIDES

Electronic states of oxides including 3d, 4d and 5d transition metals with metal ion d1 configuration were calculated using the spin-polarized DV-Xalpha method. Artificial model clusters adopted were MO6 octahedra, MO5 pyramids and square planar MO4 (M = transition metal). For the undistorted octahedron, d orbitals of the metal ion split into partially occupied levels t2g and unoccupied levels e(g). The degenerate orbitals t2g, whose components are d(xz), d(yz) and d(xy), do not have a two-dimensional character. For the octahedron whose M-O bonds in the xy(ab)-plane are elongated, metal d(xy) and oxygen p(pi) form two-dimensional half-filled states. In this case, the metal oxide probably becomes an insulator, and the p(pi) contribution to the half-filled states increases as the atomic number becomes larger. Concerning the square planar, metal d(z2), oxygen p(sigma) and metal s form the two-dimensional half-filled states. The energy separation between d and p orbitals is smaller compared to the octahedron.