FERMI-SURFACE, BONDING, AND PSEUDOGAP IN MOSI2

The electronic structure and Fermi surface of molybdenum disilicide ha s been calculated using local-density functional theory (LDA) and the linear muffin-tin orbital method (LMTO). The energy bands are analyzed in detail for their orbital character. Our explanation for the presen ce of a pseudogap after the seventh band is that the two Si s bands li e low and that there are five Mo d-Si p pair bands. The configuration is approximately Mo 4d(5) Si-2 3s(2)3p(2.5). A, explanation in terms o f directed bond-orbitals was not achieved. The calculated angular depe ndence of the extremal Fermi surface cross-section areas are in good q ualitative agreement with de Haas-van Alphen (dHvA) measurements. Howe ver, in order to obtain quantitative agreement, the Mo d(x)2-(y)2 orbi tal energy has to be shifted upwards by 0.41 eV and the Mod(xy) energy downwards by 0.20 eV. This deficiency is ascribed to the use of a loc al exchange-correlation potential.