Nonequilibrium molecular dynamics calculation of the thermal conductivity based on an improved relaxation scheme.

A nonequilibrium molecular dynamics (NEMD) method using stochastic energy injection and removal as uniform heat sources and sinks is developed to calculate the thermal conductivity. The stochastic energy is generated by a Maxwell function generator and is imposed on only a few individual molecules each time step. The relaxation of the thermal perturbation is improved compared to other NEMD algorithms because there are no localized heat source and sink slab regions in the system. The heat sources are uniformly distributed in the right half of the system while the sinks are in the left half, which leads to a periodically quadratic temperature distribution that is almost sinusoidal. The thermal conductivity is then easily calculated from the mean temperatures of the right and left half systems rather than by fitting the temperature profiles. This improved relaxation NEMD scheme is used to calculate the thermal conductivities of liquid and solid argons. It shows that the present algorithm gives accurate results with fast convergence and small size effects. Other stochastic energy perturbation, e.g., thermal noise, can be used to replace the Maxwell-type perturbation used in this paper to make the improved relaxation scheme more effective.