Repulsive water-water contacts from Cambridge Structural Database

Abstract

Water is one of the most important molecules on the Earth. Since water plays a crucial role in many life processes, it is of great importance to understand every aspect of its behavior and interactions with itself and its surroundings. It is known that water molecules can interact via classical hydrogen bonds and antiparallel interactions, with interaction energies of - 5.02 kcal/mol and -4.22 kcal/mol, respectively. Besides these attractive interactions, repulsive interactions were also noticed. In this work, we analyzed repulsive water-water contacts from the Cambridge Structural Database. All interaction energies were calculated at the so- called gold standard, i.e., CCSD(T)/CBS level of theory. It was found that among all water-water contacts, ca. 20% (2035 contacts) are repulsive with interaction energies mainly up to 2 kcal/mol. Most of these repulsive contacts do not belong to two main groups of water-water contacts. Namely, 12.8% of all repulsive contacts can be classified as classical hydrogen bonds, 2.1% to the antiparallel interactions, and the rest (85.3%) as remaining contacts. This study points out that additional attention should be paid when one deals with contacts including water or, eventually, hydrogen atoms in general.