GROUND-STATE PROPERTIES OF RUTILE - ELECTRON-CORRELATION EFFECTS

Electron-correlation effects on cohesive energy, lattice constant, and bulk compressibility of rutile are calculated using an ab initio sche me. A competition between the two groups of partially covalent Ti-O bo nds is the reason that the correlation energy does not change Linearly with deviations from the equilibrium geometry, but is dominated by qu adratic terms instead. As a consequence, the Hartree-Fock lattice cons tants are close to the experimental ones, while the compressibility is strongly renormalized by electronic correlations.