Thermostat-induced spurious interfacial resistance in non-equilibrium molecular dynamics simulations of solid-liquid and solid-solid systems

Abstract

Non-equilibrium molecular dynamics (NEMD) simulations universally rely on thermostats to control temperature. The thermostat-induced alteration in the system dynamics that enables temperature control can, however, adversely impact molecular transport across the temperature-controlled and temperature-uncontrolled regions. Here, we analyze the influence of a thermostat on thermal transport across a solid-liquid interface in a canonical setup that, owing to its generality, has been widely employed in NEMD simulations. In scenarios wherein temperature is controlled via stochastic/frictional forcing based thermostats, we find occurrence of a spurious temperature jump across the solid-liquid interface. The corresponding Kapitza length diminishes with a gradual weakening of the coupling between the thermostat and the system. Hence, we identify an optimal thermostat control parameter range over which contrasting requirements of an effective temperature control and a sufficiently low interfacial thermal resistance are simultaneously satisfied. We show that a similar disruption in thermal transport occurs in a single phase system of pure solid atoms as well. We trace the microscopic origin of the anomalous interfacial thermal resistance to a stochastic/frictional forcing-induced alteration in the force autocorrelation function. We propose a simple model consisting of an individual atom impinging in vacuo on a thermostatted solid as a computationally inexpensive alternative for determination of the control parameter range over which thermostat-induced spurious thermal resistance across a solid-liquid interface becomes significant. Our results suggest that the undesirable possibility of MD-deduced temperature jumps being misleading indicators of the interfacial Kapitza resistance could simply be eliminated through a judicious choice of the thermostat control parameter.