Stig Lundqvist

Effects of Electron-Electron and Electron-Phonon Interactions on the One-Electron States of Solids

Publisher Summary: This chapter discusses two major developments that have taken place over the past decade. First is the enormous wealth of energy band calculations that have had tremendous success in explaining the properties of specific solids, but in which the connection with first principles is not always apparent. Second is the spectacular progress of many-body theory applied to the solid state that has given a number of new results, although often of a rather general and formal nature, such as to provide the justification and a formal basis for a one-electron theory. The electron gas problem is treated in some detail here. The problem of the crystal potential is given due attention. It discusses the potential from the ion cores as well as from the valence electrons, and suggests schemes that incorporate essential exchange and correlation effects for the valence electrons. An energy band calculation that properly includes the effects of exchange and correlation describes the elementary excitations called quasi particles. Quasi-particle properties are usually discussed using the remarkable Landau theory of the Fermi liquid. This chapter gives a brief presentation of the theory and reviews the present status of calculations of the Fermi liquid parameters and how they are determined from experiments. (Less)

Photoluminescence of noble metals

We have developed an explicit model to explain the radiative recombination in noble metals, arising from transitions between electrons in the spconduction band and holes in the d-band generated by optical excitation. We find that the observed photon distribution has its shape from two competing factors. The first is due to the optics and the final density of states for the exiting photons. This is off-set by a d-band density of states factor increasing as the number of available d-states increase. We give a satisfactory account of the observed spectrum, using constant matrix elements, and find that luminescence can be used as a complementary tool to the ordinary elastic light scattering, giving detailed information about occupied and unoccupied states, provided the elastic optical constants are measured on the same sample.

Local exchange-correlation potentials

Recent advances in the many-body theory of electrons in solids and in the theory of the interacting electron gas are used to construct explicit local effective potentials which incorporate the effects of correlation and exchange. For ground state properties we consider the scheme by Hohenberg, Kohn and Sham and provide data for the effective potential μxc. For excitation energies the corresponding potential Vxc is obtained from the self-energy of an electron gas and numerical data are provided for the construction of Vxc.

New structure in the single-particle spectrum of an electron gas

Calculations of the one-electron Greens function give a single-particle spectrum where, besides the usual quasi-particles, a new peak of appreciable strength appears which corresponds to an electron coupled to real plasmons.

Screening in a spin-polarized electron liquid

Abstract Calculated exchange and correlation properties of the spin-polarized electron liquid are used in the density-functional method of Kohn and Sham to get spin-dependent, local one-body potentials and static dielectric properties. Our calculation does not support the recent conclusion by Kim and Schwartz about negative screening and shows that correlations between electrons of both spins are essential.

Non-local optical effects at metal surfaces

The non-local response of an irradiated metal surface is discussed in terms of the induced density in response to an external field. The field and the induced charge near the surface can be determined by solving Maxwell equations in the surface region and match the solution to the incoming and reflected wave in vacuum and to the asymptotic solution in the bulk of the solid. For incoming fields of wave lengths long in comparison with the extension of the surface region a key quantity is the center of gravity of the screening charge. This complex function of the frequency is important for a number of properties such as the reflectivity, the surface plasmon dispersion, image fields, van der Waals interactions between a molecule and a metal surface, etc. Considerations similar to the ones for a planar surface are also applied to the surface properties of a small metallic sphere.

Collective effects in the photoabsorption cross sections of atoms and molecules

Abstract The linear response of atoms and molecules to an external field is formulated in a self-consistent manner. The discussion centers on the collective effects in the spectral properties at frequencies higher than the first ionization edge, and their experimental manifestations. Photoabsorption and the photoelectric effect are shown to have distinct cross sections which happen to coincide only in certain approximations such as in the single-particle model. The line profile of autoionization levels is derived and compared with recent experimental observations.

ATOMIC PHOTOABSORPTION CROSS SECTIONS.

Abstract Results are reported of extensive calculations on atomic photoabsorption cross sections by the statistical method in various approximations, based on developments presented in previous papers. A closely spaced family of photoabsorption cross sections emerges which, on scaling with regard to atomic numbers, represents in an unified manner the absorption cross sections of all atoms over wide frequency ranges. A limited search into detailed spectral properties of atoms reveals everywhere some, and in certain instances strong evidence for collective effects in the response of atoms to external disturbances.

New dynamical effects in the spectra of core holes

Abstract Fluctuations of a core hole leads to new effects in core hole spectroscopy. They contribute to the relaxation and bring in new components in the satellite spectrum. In certain cases the fluctuations may lead to a rapid decay of the core hole.

Collective Aspects of Atomic Dynamics

We give a brief review of the theories describing collective dynamics of atoms, and comment on the hydrodynamic approach as well as the manybody approach based on RPA. In particular we put forward a unified approach, combining the hydrodynamical and single-particle aspects in a single theoretical framework. Some general aspects of the theory are discussed as well as a simple application to the oscillations of a spherical shell.