Simulations of liquid semiconductors using quantum forces

Evolution of cellular structures during Ge 1-x Si x single-crystal growth by means of a modified phase-field method

We have studied the evolution of cellular structures in Ge 1-x Si x single-crystal growth as a function of process parameters. Because these structures are much larger than those occurring during the solidification of metals, we developed a modified phase-field method, which is able to handle these structure within reasonable computer times using the real material parameters. The model has been tested for computing equilibrium shapes of crystals, dendritic growth, and cellular growth of Ni x Cu 1-x. We also performed classical molecular dynamics calculations in order to compute the diffusion coefficients of Si and Ge in melts of various compositions.

Ab Initio simulations of nonstoichiometric CdxTe1−x liquids

We present ab initio molecular-dynamics simulations for Cd(x)Te(1-x) liquids where the composition is nonstoichiometric. The simulations are performed following Born-Oppenheimer molecular dynamics. The required forces are obtained from a solution of the Kohn-Sham equation using ab initio pseudopotentials. We consider stoichiometries of the form: Cd(x)Te(1-x), where x=0.2, 0.4, 0.6, and 0.8. For each composition of the melt, we consider a range of temperatures near the experimentally determined liquid temperatures. We examine the microstructural properties of the melt, the viscosity, and self-diffusion properties of the liquid as a function of the stoichiometry and temperature. We also perform an analysis of the distribution of the electronic density of states in these liquids. We find that structural changes in the local order, experimentally predicted to occur when the concentration of Cd is increased, are closely related to changes in the electronic properties of the melt.

Liquid-liquid phase transitions of phosphorus via constant-pressure first-principles molecular dynamics simulations

Pressure-induced phase transitions in liquid phosphorus have been studied by constant-pressure first-principles molecular dynamics simulations. By compressing a low-pressure liquid which consists of the tetrahedral P4 molecules, a structural phase transition from the molecular to polymeric liquid (a high-pressure phase) observed in the recent experiment by Katayama et al. [Nature (London) 403, 170 (2000)] was successfully realized. It is found that this transition is caused by a breakup of the tetrahedral molecules with large volume contraction. The same transition is also realized by heating. This indicates that only the polymeric liquid can stably exist at high temperature.