All-electron local density functional study of metallic monolayers. II. Alkaline-earth metals

Abstract

For pt.I see ibid., vol.13, p.2313 (1983). The electronic structures and cohesive energies of hexagonal monolayers of the alkaline-earth metals Be to Ba are studied in terms of self-consistent all-electron local density functional calculations using the full-potential linearised augmented plane-wave method for thin films. The energy band structures of the 'light' atoms Be and Mg show wide s bands overlapping with pz bands without any pronounced spectral features in their densities of states. In contrast, the 'heavy' alkaline-earth metals Ca, Sr and Ba are characterized by much narrower s bands and by increasingly sharper features in their densities of states originating from d-like states. Thus, the densities of states at the Fermi energy for the Be and Mg monolayers are low and increase dramatically for Ca, Sr and particularly Ba. In contrast to recent Hartree-Fock results, the author's study shows that the Be monolayer is metallic. The work functions of the monolayers are found to be about 0.2 eV higher than the experimental values for the clean metal surface. The high cohesive energy of Be is explained by the absence of p-core electrons and the admixture of pi bonding. Magnesium is found to form the most weakly bound alkaline-earth monolayer whereas those of Ca, Sr and Ba are stabilised by the contribution of d states.