Molecular dynamics simulation of the structure and diffusion properties ofliquid silicon

Using molecular-dynamics methods and the activation-relaxation technique, w e have investigated the inherent structure and diffusion properties of liqu id silicon. With increasing density, the 52 degrees and 60 degrees peaks (a ttributed to long bonds) in the bond-angle distribution functions decrease in height, while the spread main peak. (mainly related to the bonds contain ing covalent character) increases and moves towards the tetrahedral angle. The change in density does not give rise to a clear change in the diffusion constants. With the change of temperature, the diffusion coefficients obta ined from the. average mean-square displacement can be fitted by Arrhenius equation. The fit yields an activation energy of 0.92 eV and a pre-exponent ial factor of 30.8 x 10(-3) cm(2) s(-1). However, the activation energy, wh ich is determined from the activation-relaxation technique using a Metropol is accept-reject criterion with a fictitious temperature of 0.5 eV, is in t he range of 0.22 to 1.0 eV and shows a steep increase at low temperature. T he very large pre-exponential factor suggests that the interatomic forces o btained from the Tersoff potential are very strong. The information obtaine d in this paper is consistent to some extent with the recent experimental r esults of some physical properties of liquid silicon.