Towards a first-principles implementation of density-functional theory at a metal surface

Abstract

The implementation of the density-functional scheme requires the knowledge of the exchange and correlation potential, Vxc, as a functional of the electron density. In the local-density approximation (LDA) this potential becomes a function of the local value of the density. This ansatz breaks down qualitatively at a surface because of its neglect of long-range electron-electron correlations in the presence of strong charge inhomogeneity. This breakdown is of relevance in the context of various surface spectroscopies. We outline a scheme for going beyond the LDA without invoking gradient expansions. This scheme is based on establishing an interrelation between density-functional theory and many-body perturbation theory. In this scheme Vxc is obtainable from the knowledge of the electron self-energy Σxc. We solve an exact integral equation relating these two quantities for the electron–gas surface with use of the GW approximation for the self-energy. We establish a “nonlocal” relation between Vxc and the electron density which allows us to carry out nonlocal density-functional calculations with the same ease as LDA-based calculations. We present results of the first application of our method for the case of Al and Pd surfaces. In addition, we report on work in progress devoted to a detailed comparison of the density-functional and quasiparticle pictures of electronic excitations at a metal surface. © 1992 John Wiley & Sons, Inc.