Chemical trends in gold alkali alloys: A density functional theory study on stability and charge transfer Part I: Gold alkali alloys of the formula MAu

Abstract

Gold alkali alloys have roused the interest of both chemists and physicists since their discovery half a century ago. While experimentalists tried to synthesize more and more new alloys filling up the homologous rows of compounds, the theoreticians tried to understand the astonishing properties of these alloys by doing more and more exact calculations. The experimental and theoretical breakthroughs, however, took place only a few years ago, when single crystals could be synthesized and examined and new powerful ab initio programs and supercomputers were developed. Within the framework of density functional theory (in the local density approximation together with norm-conserving, scalar-relativistic pseudopotentials) we calculate the structural properties of MAu alloys comparing the stabilities of these alloys in NaCl, CsCl and NaTl structures with each other and with experiment. Moreover, we examine the electronic valence charge densities of these alloys and investigate the charge transfer in them by employing the concept of zero-flux surfaces. We find that charge transfer occurs from the alkali to the gold atom as expected. Moreover, we find a change from ionic to metallic binding between NaAu and LiAu.