O. Gunnarsson

The GW method

Calculations of ground-state and excited-state properties of materials have been one of the major goals of condensed matter physics. Ground-state properties of solids have been extensively investigated for several decades within the standard density functional theory. Excited-state properties, on the other hand, were relatively unexplored in ab initio calculations until a decade ago. The most suitable approach up to now for studying excited-state properties of extended systems is the Green function method. To calculate the Green function one requires the self-energy operator which is non-local and energy dependent. In this article we describe the GW approximation which has turned out to be a fruitful approximation to the self-energy. The Green function theory, numerical methods for carrying out the self-energy calculations, simplified schemes, and applications to various systems are described. Self-consistency issue and new developments beyond the GW approximation are also discussed as well as the success and shortcomings of the GW approximation.

Superconductivity in fullerides

Experimental studies of the superconductive properties of fullerides are briefly reviewed. Theoretical calculations of the electron-phonon coupling, in particular for the intramolecular phonons, are discussed extensively. The calculations are compared with coupling constants deduced from a number of different experimental techniques. It is discussed why A{sub 3}C{sub 60} are not Mott-Hubbard insulators, in spite of the large Coulomb interaction. Estimates of the Coulomb pseudopotential {mu}{sup {asterisk}}, describing the effect of the Coulomb repulsion on the superconductivity, as well as possible electronic mechanisms for the superconductivity, are reviewed. The calculation of various properties within the Migdal-Eliashberg theory and attempts to go beyond this theory are described. {copyright} {ital 1997} {ital The American Physical Society}

Electronic structure of cerium and light rare-earth intermetallics

Abstract We give an overview of the use of the impurity Anderson Hamiltonian to describe the spectroscopic and low-energy thermodynamic properties of cerium intermetallics, with emphasis on interpreting 4f photoemission spectra. We show Ce valence-band resonant photoemission, Bremsstrahlung isochromat and 3d X-ray photoemission spectra for CeRu2, CeNi2, CeIr2 and CeAl, and give a complete theoretical analysis of the spectra. We summarize the relation between the large and small energy scale properties. For each system, all the spectra, as well as the static magnetic susceptibility and Kondo temperature, can be described by the model using essentially the same parameters. We also present details of resonant photoemission spectra for five other cerium compounds, CeSi2, CeOs2, CePd3, CeCo2 and CeNi5, and discuss generally the problem of obtaining the experimental 4f spectrum. Alternative theories of 4f photoemission are examined critically and we give applications of the Anderson Hamiltonian theory to CeAl2,...

Colloquium : Saturation of electrical resistivity

Resistivity saturation is observed in many metallic systems with large resistivities---when the resistivity has reached a critical value, its further increase with temperature is substantially reduced. This typically happens when the apparent mean free path is comparable to the interatomic separations---the Ioffe-Regel condition. Recently, several exceptions to this rule have been found. This colloquium first reviews experimental results and early theories of resistivity saturation. It then describes more recent theoretical work, addressing cases both where the Ioffe-Regel condition is satisfied and where it is violated. In particular, the authors show how the (semiclassical) Ioffe-Regel condition can be derived quantum mechanically under certain assumptions about the system and why these assumptions are violated for high-

Mott transition in degenerate Hubbard models: Application to doped fullerenes.

{T}_{c}

Alkali-doped fullerides : narrow-band solids with unusual properties

cuprates and alkali-doped fullerides.

Electrons, phonons, and their interaction in YBa2Cu3O7

The Mott-Hubbard transition is studied for a Hubbard model with orbital degeneracy

Correlation effects on core level spectra of adsorbates

N

Exchange and correlation in inhomogeneous electron systems

, using a diffusion Monte Carlo method. Based on general arguments, we conjecture that the Mott-Hubbard transition takes place for

Electron-phonon interaction in the t-J model

\frac{U}{W}\ensuremath{\sim}\sqrt{N}