Band Structure of Cubic and Hexagonal Argon

A pseudopotential calculation of the band structure of both cubic-close-packed and hexagonal-close-packed solid argon is presented. The pseudopotential form factor is obtained by fitting energy gaps to Mattheiss's augmented-plane-wave calculation. The direct gaps obtained are 1.03 Ry in the cubic phase and 0.84 Ry in the hexagonal plane, i.e., a sizable reduction is found in the hexagonal structure. The hexagonal valence band splits into two subbands of $p_z$ and $p_x-p_y$ character with an energy gap clearly appearing between them; the $p_z$-like band lies higher in energy and constitutes the top of the valence band. Several other features of the structures are discussed. Convergence of both calculations is checked to be about 0.01 Ry. Sensitivity of the results to changes in the form factors is also discussed.