Vl. N. Antonov

Valence band excitations in V2O5

We present a joint theoretical and experimental investigation of the electronic and optical properties of vanadium pentoxide. Electron energy-loss spectroscopy in transmission was employed to measure the momentum-dependent loss function. This in turn was used to derive the optical conductivity, which is compared to the results of band structure calculations. A good qualitative and quantitative agreement between the theoretical and the experimental optical conductivity was observed. The experimentally observed anisotropy of the optical properties of V_2O_5 could be understood in the light of an analysis of the theoretical data involving the decomposition of the calculated optical conductivity into contributions from transitions into selected energy regions of the conduction band. In addition, based upon a tight binding fit to the band structure, values are given for the effective V3d_xy-O2p hopping terms and are compared to the corresponding values for alpha-NaV_2O_5.

Fermi surface, bonding, and pseudogap in MoSi2

Abstract The electronic structure and Fermi surface of molybdenum disilicide has 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 presence of a pseudogap after the seventh band is that the two Si s bands lie low and that there are five Mo d-Si p pair bands. The configuration is approximately Mo 4d5 Si2 3s2 3p2.5. An explanation in terms of directed bond-orbitals was not achieved. The calculated angular dependence of the extremal Fermi surface cross-section areas are in good qualitative agreement with de Haas-van Alphen (dHvA) measurements. However, in order to obtain quantitative agreement, the Mo dx2−y2 orbital energy has to be shifted upwards by 0.41 eV and the Mo dxy energy downwards by 0.20 eV. This deficiency is ascribed to the use of a local exchange-correlation potential.

Electronic structure and x-ray magnetic circular dichroism in (Ge,Mn)Te diluted magnetic semiconductors

The electronic structure of the (Ge,Mn)Te diluted magnetic semiconductors was investigated theoretically from rst principles, using the fully relativistic Dirac linear mufn-tin orbital (LMTO) band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA) as well as the LSDA+U method. The x-ray magnetic circular dichroism (XMCD) spectra of (Ge,Mn)Te DMSs at the Mn L2;3 edges are investigated theoretically from rst principles. The origin of the XMCD spectra in the compound is examined. The calculated results are compared with available experimental data.

THE FERMI SURFACES OF La2−xSrxCuO4 AND YBa2Cu3O7

The theoretical investigation of the Fermi surface (FS) and constant-energy one near the Fermi energy of La2−xSrxCuO4 and YBa2Cu3O7 is the aim of this work.