Non-equilibrium molecular dynamics calculation of heat conduction in liquid and through liquid-gas interface

Abstract

This paper presents a new algorithm for non-equilibrium molecular dynamics, where a temperature gradient is established in a system with periodic boundary conditions. At each time step in the simulation, a fixed amount of energy is supplied to a hot region by scaling the velocity of each particle in it, subject to conservation of total momentum. An equal amount of energy is likewise withdrawn from a cold region at each time step. Between the hot and cold regions is a region through which an energy flux is established. Two configurations of hot and cold regions are proposed. Using a stacked layer structure, the instantaneous local energy flux for a 128-particle Lennard-Jones system in liquid was found to be in good agreement with the macroscopic theory of heat conduction at stationary state, except in and near the hot and cold regions. Thermal conductivity calculated for the 128-particle system was about 10% smaller than the literature value obtained by molecular dynamics calculations. One run with a 1024-particle system showed an agreement with the literature value within statistical error (1–2%). Using a unit cell with a cold spherical region at the centre and a hot region in the perimeter of the cube, an initial gaseous state of argon was separated into gas and liquid phases. Energy fluxes due to intermolecular energy transfer and transport of kinetic energy dominate in the liquid and gas phases, respectively.