Showing papers by "Sergey Y. Savrasov published in 1998"

Electron-energy-loss spectra and the structural stability of nickel oxide: An LSDA+U study

Abstract: We demonstrate how by taking better account of electron correlations in the $3d$ shell of metal ions in nickel oxide it is possible to improve the description of both electron energy loss spectra and parameters characterizing the structural stability of the material compared with local spin density functional theory.

Electronic Structure and Elastic Properties of Strongly Correlated Metal Oxides from First Principles: LSDA + U, SIC‐LSDA and EELS Study of UO2 and NiO

Abstract: We compare experimentally observed electron energy loss spectra (EELS) of uranium dioxide UO 2 and nickel monoxide NiO with the results of ab-initio calculations carried out by using a method combining the local spin density approximation and the Hubbard U term (the LSDA + U method). We show that by taking better account of strong Coulomb correlations between electrons in the 5f shell of uranium ions in UO 2 and in the 3d shell of nickel ions in NiO it is possible to arrive at a better description of electron energy loss spectra, cohesive energies and elastic constants of both oxides compared with local spin density functional theory. For NiO we also compare the LSDA + U results and EELS spectra with a self-interaction corrected LSDA calculation.

Linear Response Calculations of Spin Fluctuations

Abstract: A variational formulation of the time-dependent linear response based on the Sternheimer method is developed in order to make practical ab initio calculations of dynamical spin susceptibilities of solids. Using gradient density functional and a muffin-tin-orbital representation, the efficiency of the approach is demonstrated by applications to selected magnetic and strongly paramagnetic metals. The results are found to be consistent with experiment and are compared with previous theoretical calculations.

Electron-phonon coupling and properties of doped BaBiO 3

Abstract: We report density-functional calculations based on the local-density approximation (LDA) of the properties of doped barium bismuthates. Using the linear-response approach developed in the framework of the linear muffin-tin-orbital method the phonon spectrum of the ${\mathrm{Ba}}_{0.6}{\mathrm{K}}_{0.4}{\mathrm{BiO}}_{3}$ system is calculated and is compared with the results of the neutron-diffraction measurements. The effect of doping in the calculation is modeled by the virtual crystal and mass approximations. The electron-phonon coupling constant $\ensuremath{\lambda}$ is then evaluated for a grid of phonon wave vectors using the change in the potential due to phonon distortion found self-consistently. A large coupling of the electrons to the bond-stretching oxygen vibrations and especially to the breathinglike vibrations is established. Also, a strongly anharmonic potential well is found for the tiltinglike motions of the oxygen octahedra. This mode is not coupled to the electrons to linear order in the displacements; therefore an anharmonic contribution to $\ensuremath{\lambda}$ is estimated using the frozen-phonon method. Our total (harmonic plus anharmonic) $\ensuremath{\lambda}$ is found to be 0.34. This is too small to explain high-temperature superconductivity in ${\mathrm{Ba}}_{0.6}{\mathrm{K}}_{0.4}{\mathrm{BiO}}_{3}$ within the standard mechanism. Finally, based on standard LDA and LDA+$U$ like calculations, a number of properties of pure ${\mathrm{BaBiO}}_{3}$ such as tilting of the octahedra, breathing distortion, charge disproportionation, and semiconducting energy gap value is evaluated and discussed in connection with the negative-$U$ extended Hubbard model frequently applied to this compound.

Linear Response Calculations of Spin Fluctuations

Abstract: A variational formulation of the time-dependent linear response based on the Sternheimer method is developed in order to make practical ab initio calculations of dynamical spin susceptibilities of solids. Using gradient density functional and a muffin-tin-orbital representation, the efficiency of the approach is demonstrated by applications to selected magnetic and strongly paramagnetic metals. The results are found to be consistent with experiment and are compared with previous theoretical calculations.

Buckling and d-Wave Pairing in HiTc-Superconductors

Abstract: Abstract We have investigated whether the electron–phonon interaction can support a d-wave gap anisotropy. On the basis of models derived from LDA calculations, as well as LDA linear-response calculations, we argue that this is the case for materials with buckled or dimpled CuO 2 planes for the so-called buckling modes, which involve out-of-plane movements of the planar oxygen atoms.