Hydrogen bonds in computer-simulated water

Geometric, energetic and dynamic criteria used for the search of hydrogen bonds in simulated water are discussed. Molecular dynamics computer simulation of a water droplet and bulk liquid water with periodic boundary conditions demonstrated that distribution of hydrogen bond lifetimes is very broad and their values may be as great as 20 ps. This means that long-living complexes composed of two or three molecules exist in liquid water. Switching of hydrogen bonds from one partner to another may be realized via formation of a bifurcated hydrogen bond, but a free, not involved in hydrogen bonding OH group may be a transition state as well. About half of the time every molecule is surrounded by four hydrogen-bonded molecules being a proton donor for the two and an acceptor for the other two. The lifetime of this configuration may achieve 2.6 ps. (C) 1999 Elsevier Science B.V. All rights reserved.