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A Nosé-Hoover Thermostat Adapted to a Slab Geometry

Maćkowiak S., Pieprzyk S., Brańka A. C., Heyes D. M.

Computational Methods in Science and Technology

2017

Vol. 23, No. 3

211--218

A Nosé-Hoover (NH) type thermostat is considered for Molecular Dynamics (MD) simulations of confined systems. This is based on a generalised velocity of the same generic form as the NH thermostat of Allen and Schmid, [Mol. Sim. 33, 21 (2007)]. An unthermostatted confined region is sandwiched between two walls which are thermostatted. No external shearing is imposed. Non-equilibrium Molecular Dynamics (NEMD) simulations were carried out of the time evolution of the wall and confined region temperature after a jump in temperature of the walls. Relaxation of the confined region temperature to the target value was found to be typically slower than that of the wall. An analysis of the system parameter dependence of the lag time, , and departures from what would be expected from Fourier’s law suggest that a boundary transmission heat flux bottleneck is a significant factor in the time delay. This delayed thermal equilibration would therefore become an important factor when a time-dependent (e.g., oscillatory) temperature or shearing of the walls is implemented using NEMD. Adjustments between the response time of the wall thermostat should be made compatible with that of the rest of the system, to minimise its effects on the observed behaviour.

Configurational Temperature and Monte Carlo Simulations

Brańka A. C., Pieprzyk S.

Computational Methods in Science and Technology

2010

Vol. 16, No. 2

119-125

Two configurational temperature expressions are investigated from the point of view of their utility as a diagnostic tool for Monte Carlo (MC) simulations. The MC calculations were performed for systems of spherically symmetric particles in the bulk and in a channel. Different density and system size conditions are considered. It is shown that the configurational temperature based on the ratio of two averages of the force functions can serve as a suitable method for calculating the temperature for the MC simulation. This configurational temperature can signal the presence of random number correlations and can serve as a cross-check formula in MC studies of strongly confined systems.