Nonequilibrium molecular dynamics simulation of shear viscosity by a uniform momentum source-and-sink scheme

A uniform momentum source-and-sink scheme of nonequilibrium molecular dynamics (NEMD) is developed to calculate the shear viscosity of fluids in this paper. The uniform momentum source and sink are realized by momentum exchanges of individual atoms in the left and right half systems, like the reverse nonequilibrium molecular dynamics (RNEMD) method [20] [Müller-Plathe, Phys. Rev. E, 49 (359), 1999]. This method has all features of RNEMD. In addition, the present momentum swap strategy maximizes the perturbation relaxation and eliminates the boundary jumps, which often harm other NEMD methods greatly. With periodic boundary conditions quadratic velocity profiles can be constructed and from the mean velocities of the right and left half systems the shear viscosity can be easily extracted. The scheme is tested on Lennard-Jones fluids over a wide range of state points (temperature and density), momentum exchange intervals and system sizes. It is demonstrated that the present approach can give reliable results with fast convergence by properly selecting the simulation parameters, i.e. particle number and exchange interval.