Title: Effects of translational and rotational degrees of freedom on the properties of model water
Author(s):

	T. Mohorič (Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia) ,
	B. Hribar-Lee (Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia) ,
	V. Vlachy (Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia)

Molecular dynamics simulations with separate thermostats for rotational and translational motions were used to study the effects of these degrees of freedom on the structure of water at a fixed density. To describe water molecules, we used the SPC/E model. The results indicate that an increase of the rotational temperature, T_R, causes a significant breaking of the hydrogen bonds. This is not the case, at least not to such an extent, when the translational temperature, T_T, is raised. The probability of finding an empty spherical cavity (no water molecule present) of a given size, strongly decreases with an increase of T_R, but this only marginally affects the free energy of the hydrophobe insertion. The excess internal energy increases proportionally with an increase of T_R, while an increase of T_T yields a much smaller effect at high temperatures. The diffusion coefficient of water exhibits a non-monotonous behaviour with an increase of the rotational temperature.

Key words: water structure, degrees of freedom, molecular dynamics
PACS: 05.20.Jj, 05.70.Ln, 61.20.Ja, 61.20.Qg, 61.25.Em

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