The direct method for computing thermal conductivity in nonequilibrium molecular dynamics gives rise to an artificial Kapitza resistance at the interface between thermostatted and unthermostatted regions. This resistance, which depends on the system size and the thermostat parameters, creates discontinuous jumps in the temperature and heat flux across the interface and therefore affects the measured thermal conductivity. In this paper, we propose a phenomenological relation for the Kapitza resistance that can be used to extract a value for the bulk thermal conductivity, which is independent of the system size and thermostat details. The paper also provides insight into the Kapitza phenomenon resulting from numerical thermostatting.
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