First-principles simulation of liquid silicon using Langevin dynamics with quantum interatomic forces

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Abstract
We present a method capable of performing molecular-dynamics simulations on complex systems using ab initio pseudopotentials. Here, we apply this method to examine the properties of liquid silicon. Our simulation method does not use fictitious electron dynamics; at each time step the interatomic forces are computed quantum mechanically. The liquid is prepared by melting the crystal and thermalizing the resulting liquid via Langevin dynamics. Once the desired temperature has been achieved, the Langevin ‘‘viscosity’’ term is turned off and dynamical properties may be examined. Our procedure has a number of advantages over other techniques. For example, large time steps can be used with this method. Metallic systems such as liquid silicon can be handled in a straightforward fashion. No ad hoc dynamics or Nosé dynamics need be employed to equilibrate the system to the desired temperature. Results for liquid silicon including the pair correlation function, density of states, and self-diffusion parameters are presented and compared to previous calculations and to experiment.