Electron Correlations and Materials Properties

Over the last thirty years or so, the attempts to identify the electronic origins of materials properties have proceeded along two distinct and apparently divergent methodologies. On the one-hand, so-called single-particle methods are based on the study of a single electron moving in an effective field formed by the other electrons and the nuclei in the system. Band theory, as this approach is referred to, has had impressive successes in determining the equilibrium properties, such as structural stability, volume, and charge densities, of specific materials, notably metals. Today, even coherent phase diagrams (based on a single underlying lattice) for binary metallic alloys can be studied with considerable accuracy. In spite of its serious and well-understood limitations regarding the handling of correlations, band theory has been embraced by the materials scientist. Its single-particle nature endows the method with an economy of concepts which leads to a clear identification of mechanisms driving physical behavior at the electronic level. This perceived clarity often tends to override legitimate concerns regarding the validity of the method or its ability to correctly identify the mechanisms in the first place. The alternative methodology pursued in the study of quantum systems consists of what can be referred to as conventional many-body theory. This methodology is based on attempts to study explicitly the effects of interparticle correlations using a number of different formal approaches, including but not limited to, perturbation methods, Green-function equation of motion methods, configuration interactions, quantum Monte Carlo, and others.

Table of Contents:
Opening remarks.- 1: Experimental Indications of Correlation Effects in Materials.- Experimental studies of electron correlation effects in solids.- Photoemission in strongly correlated crystalline f-electron systems: A need for a new approach.- Heavy electron phenomena.- Lattice effects in the light actinides.- Anomalous magnetic and related electronic properties of uranium intermetallic compounds.- The role of selected f ions in the suppression of high-Tcsuperconductivity.- An investigation of the magnetic fluctuations above and below Tcin the heavy Fermion superconductor UPd2A13.- Non-Fermi liquid properties and exotic superconductivity in CeCu2Si2and (UTh)Be13.- Onset of magnetism and non-Fermi-liquid behavior in UTX compounds.- Non-Fermi liquid behavior in U3-xNi3Sn4-ysingle crystals.- 2: Phenomenological Studies of Correlation Effects.- Introductory overview and heavy-Fermion phenomenology.- Magnetic and thermodynamic properties of the 3-d Anderson lattice Hamiltonian.- Narrow-band effects in rare-earths and actinides: Interaction between the Kondo effect and magnetism.- Consequences of having two kinds of f-electrons for strongly correlated electron systems as treated by a synthesis of many-body theory and electronic structure.- Effect of disorder in the periodic Anderson model.- Dynamical electron correlations in metals: TB-LMTO and multiband Hubbard Hamiltonian.- 3:Ab InitioStudies of Correlation Effects.- Exchange and correlation in atoms, molecules, and solids: The density functional picture.- On time-independent density-functional theories for excited states.- Quasiparticle and optical excitations in solids and clusters.- Ab initiostudies of electronic excitations in real solids 329.- Pair densities, particle number fluctuations, and a generalized density functional theory.- The two-particle picture and electronic structure calculations.- Orbital functionals in static and time-dependent density functional theory.- Understanding electronic wave functions.- Density functional theory for the study of single-molecule electronic systems.- Density functional theory for a single excited state.- Construction of an accurate self-interaction-corrected correlation energy functional based on an electron gas with a gap.- Towards new approximations for the exchange-correlation functional using many-body perturbation theory.- Electronic structure and magnetism of itinerant 5f ferromagnets URhSi and URhGe.- Pressure-induced phase transitions in alkali halides: HF and DFT study.- A Quantum Monte Carlo study of the exchange-correlation hole in silicon atom and system-averaged correlation holes of second row atoms.- Strongly correlated electrons: Dynamical vertex renormalization.- Correlation effects on stability in Pu metal and its alloys.- General discussion I.- General discussion II.- List of Participants.