Electronic Excitations and Correlation Effects in Metals

TL;DR

This paper reviews recent progress in understanding electronic excitations in metals, emphasizing the importance of correlation effects beyond mean-field theory and proposing a numerical algorithm for self-consistent Green's function calculations.

Contribution

It introduces a fully conserving, finite-temperature numerical scheme for solving the Dyson equation incorporating dynamical correlations and band structure effects from first principles.

Findings

Correlation effects are significant even in weakly-correlated metals.

Band structure influences the electronic excitation spectra.

Self-consistent calculations highlight the importance of many-body effects.

Abstract

Theoretical descriptions of the spectrum of electronic excitations in real metals have not yet reached a fully predictive, "first-principles" stage. In this paper we begin by presenting brief highlights of recent progress made in the evaluation of dynamical electronic response in metals. A comparison between calculated and measured spectra - we use the loss spectra of Al and Cs as test cases - leads us to the conclusion that, even in "weakly-correlated" metals, correlation effects beyond mean-field theory play an important role. Furthermore, the effects of the underlying band structure turn out to be significant. Calculations which incorporate the effects of both dynamical correlations and band structure from first principles are not yet available. As a first step towards such goal, we outline a numerical algorithm for the self-consistent solution of the Dyson equation for the one-particle Green's function. The self-energy is evaluated within the shielded-interaction approximation of Baym and Kadanoff. Our method, which is fully conserving, is a finite-temperature scheme which determines the Green's function and the self-energy at the Matsubara frequencies on the imaginary axis. The analytical continuation to real frequencies is performed via Pade approximants. We present results for the homogeneous electron gas which exemplify the importance of many-body self-consistency.