Total energies in Se. I. The trigonal crystal

The equilibrium crystal structure (lattice constants and chain radius) of trigonal selenium, a molecular crystal, are determined by minimizing the total energy, as calculated in the local-density and frozen-core approximations. The cohesive energy and ${\Gamma }_1\left(A_1\right)$ phonon frequency are also computed. Comparison with experiment shows excellent agreement for intrachain properties, and satisfactory agreement for interchain properties. This indicates that ab initio local-density total-energy calculations are viable for the case of molecular crystals.