Consistency of geometrical definitions of hydrogen bonds based on the two-dimensional potential of mean force with respect to the time correlation in liquid water over a wide range of temperatures

Abstract

We examine the temperature dependence of the hydrogen-bond (H-bond) dynamics in supercooled water through the molecular dynamics (MD) simulations using the TIP4P/2005 model. First, we investigate the two-dimensional (2D) potential of mean force (PMF) for the H-bond definition using a pair of distance and angle coordinates between two water molecules. Specifically, we utilize four combinations of the geometrical variables, R-β, r-α, r-γ, and r-ψ, where R and r are the intermolecular O-O and O-H distances, respectively. β and α represent the angles of O-OH and O-HO, respectively, while ψ and γ are angles introduced in terms of the intermolecular O-H vector and the HOH plane of the H-bond acceptor. The consistency among the four definitions of H-bond was then examined by identifying the saddle point on the 2D PMF and analyzing the time correlation function of H-bond. It was found over a wide range of temperatures from the ambient to supercooled that the H-bond definition does not affect the long-time H-bond correlation function and correspondingly, the H-bond lifetime τHB.