α-gallium: A metallic molecular crystal

Abstract

We present a first-principles theoretical study of the atomic and electronic structures, and of the zero-temperature phases of gallium. The picture of \ensuremath{\alpha}-Ga that emerges is of a metallic molecular crystal with a strong ${\mathrm{Ga}}_{2}$ covalent bond and weaker intermolecular forces. This picture is supported in detail by the charge density, the electronic structure, and differential bond stretching under pressure. Anomalous features of \ensuremath{\alpha}-Ga, such as the Knight shift, anisotropic Fermi-surface effects, and optical absorption find a consistent explanation. Accurate x-ray measurements should reveal the ${\mathrm{Ga}}_{2}$ covalent bonds.