MOLECULAR-DYNAMICS AT CONSTANT TEMPERATURE

Molecular dynamics simulations at constant temperature of molecules with internal degrees of freedom have been analysed by simulating alkanes at different temperatures and densities. The dynamics of a single thermostated butane molecule is in general irregular. The irregular behaviour, however, are not sufficiently chaotic for a fully statistical description. When the thermostat is applied to a fluid of butane molecules we only obtain a biased sampling for a low fluid density and only for thermostat relaxation times close to the fast intramolecular bond- and angle vibration times. The overall behaviour indicates that the anharmonic energy terms play a crucial role for the efficiency of the thermostat. © 1990 IOP Publishing Ltd.