Canonical Molecular Dynamics of Molecules with Internal Degrees of Freedom

Canonical molecular dynamics simulations 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 not fully chaotic, even at high temperatures, and it tends to behave regular for large thermostat relaxation times. 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.