Vibrational motions of hydrogen bonds from the short time relative pair dynamics

Abstract

The short time dynamics of pairs of water molecules, initially lying in the first coordination shell, is investigated via molecular dynamics simulation. The introduction of the generalized time-dependent pair distribution function allows to obtain a relationship between the dynamics and the local structure. The relationship explains the different short time behaviors between the hydrogen-bonded molecules and the structural defects, and the lack of the free flight time dependence of the mean-square distance. The centers of mass vibrational motion of hydrogen-bonded molecules influences the relative pair dynamics beyond the short time expansion. An approach, based on the instantaneous normal modes theory, is proposed to derive the vibrational motion of the hydrogen bonds. Its general applicability is stressed and the particular relevance for studying systems whose dynamics is determined by strong oriented interactions is suggested.