On the centre of mass velocity in molecular dynamics simulations

Abstract

Molecular dynamics simulations are performed on a fluid at supercritical conditions to analyze the effect that the velocity of centre of mass (VCOM) of the system has on temperature and phase stability. Standard rescaling velocities and Nosé-Hoover chains of thermostats methods are used to carry out simulations on Square Well, Lennard-Jones and Soft Primitive potential models. Removing the VCOM at the beginning or during the simulation is not required for the Nosé-Hoover chain of thermostats to keep the correct temperature of the system, however, it is fundamental to keep null the VCOM when the traditional rescaling velocity scheme is used. It is shown that if the VCOM is removed only at the beginning of the simulation the internal and external temperatures are not the same for very long simulations and the fluid becomes a solid. The temperatures and physical properties obtained using the Nosé-Hoover chain method are the same as those obtained by removing the VCOM during the simulation in the rescaling velocity procedure.