Properties of liquid arsenic: A theoretical study

Various properties of liquid arsenic are calculated within the formalism of the quantum local-density-functional approximation, using the molecular-dynamics method proposed by Car and Parrinello. The structure of liquid arsenic is found to be similar to its ground-state, rhombohedral crystal structure, with coordination number 3 (in agreement with neutron-diffraction experiments), and has similar bond-angle, pyramid-height, and pyramid-angle distribution functions. Liquid arsenic is found to be a semiconductor with an energy gap of 0.15 eV. These results are consistent with the picture that the threefold coordination arises from a Peierls-type distortion from a sixfold-coordinated, simple-cubic-like structure. High-density and high-temperature properties are also studied, and it is shown that a crossover to a sixfold-coordinated metallic liquid will occur at high density, but not at high temperature. The structural properties of liquid arsenic are also studied by simulations employing pair potentials derived from second-order perturbation theory, which work surprisingly well, while showing small but significant differences from the ab initio simulations.