Beryllium-hydrogen ultrathin films. I. Metallic behavior of theBeH2monolayer

Equilibrium lattice parameters, total energies, the in-plane energy second derivative, and Kohn-Sham energy bands for the ${\mathrm{BeH}}_2$ 1-layer are determined by all-electron, full-potential, local-density-functional calculations. The ${\mathrm{BeH}}_2$ 1-layer is predicted to be metallic, in contrast with a previous Hartree-Fock calculation which predicted large-gap insulating behavior. By direct calculation, this disparity is traced to basis-set restrictions in the Hartree-Fock calculation that drive the highly localized Be surface state into the conduction band. The minimum-energy lattice constant ${\mathit{a}}_{\mathit{s}}$ (i.e., the square edge that is twice the Be-H distance) for the ${\mathrm{BeH}}_2$ 1-layer is 5.51 a.u. The calculated H-H distance is 3.90 a.u., lower than Switendick’s empirical criterion (3.97 a.u.) for stable metal hydrides but still well above the 3.40 a.u. involved in Overhauser’s conjecture about superconductivity in ${\mathrm{LiBeH}}_3$.