Using molecular-dynamics and activation-relaxation techniques, the inherent structure and diffusion properties of liquid silicon were investigated (table 30). With increasing density, the 52° and 60° peaks (attributed to long bonds) in the bond-angle distribution functions decreased in height, while the spread main peak (mainly related to bonds having some covalent character) increased and moved towards the tetrahedral angle. The change in density did not give rise to a clear change in the diffusion constants. With changing temperature, the diffusion coefficients deduced from the average mean-square displacement could be fitted by an Arrhenius equation. The fit yielded the relationship:

D(cm2/s) = 30.8 x 10-3exp[-0.92(eV)/kT

The activation energy which was determined from the activation-relaxation technique using a Metropolis accept-reject criterion with a fictitious temperature of 0.5eV, was in the range of 0.22 to 1.0eV and exhibited a steep increase at low temperature. The very large pre-exponential factor suggested that the interatomic forces obtained from the Tersoff potential were very strong.

Molecular-Dynamics Simulation of the Structure and Diffusion Properties of Liquid Silicon. Zhu, Z.G., Liu, C.S.: Physical Review B, 2000, 61[14], 9322-6

Table 30

Diffusivity of liquid Si