Structure and dynamics of liquid selenium

First-principles molecular-dynamics simulations of liquid selenium at the temperatures 570, 870, and 1370 K are presented. It is shown that calculations based on the local-density approximation are not satisfactory, because they seriously overestimate the equilibrium density of the solid and the liquid, and they give only rough agreement with measured structural data when the liquid is simulated at the experimental density. The inclusion of gradient corrections mitigates these problems, and most of the results presented are based on the generalized gradient approximation. The simulations are used to investigate the three-dimensional structure of the liquid, and results are presented for the bond-angle and dihedral-angle distributions, the concentration and structure of different ${\mathrm{Se}}_{n}$ rings, and the temperature-dependent length of chains. The self-diffusion constants and vibrational spectra are shown to agree satisfactorily with experimental data, and an analysis of the lifetime of covalent bonds gives insight into the diffusion mechanism. The electronic density of states of the liquid displays all the features known for the solid, and this indicates that the electronic structure changes little on melting.