Bonding energetics of metals: Explanation of trends

Abstract

Bonding energetics of elemental metals are explained by a uniform electron-gas model that has been modified to be in mechanical equilibrium. The trends in the work functions, cohesive energies, and chemical potentials are explained semiquantitatively. The same model explains the surface energies of the simple metals; however, it fails qualitatively for the surface energies of the transition metals. The approach retains the simplicity of the uniform electron gas; its only input parameter is the average electron density. Basically, we change the definition of the uniform electron gas slightly, so that the electron gas is in mechanical equilibrium at any particular specified density. The change is a rule for splitting the constant background charge when jellium is cleaved. The trends in the energetics of metals result. The concept of a bonding valence will be defined in order to treat the transition metals in terms of a uniform electron gas. Further, the model, due to its simplicity, may serve as a theoretical laboratory for the study of bonding in metals. For example, it presents the possibility of a nonperturbative calculation of the surface energy of the simple metals beyond the local-density approximation. It is also expected to be a better starting point than jellium for modeling the dynamical surface excitations of metals.