Contribution of the Covalent Component of the Hydrogen-Bond Network to the Properties of Liquid Water

Abstract

Many remarkable properties of liquid water originate from the ability of its molecules to form hydrogen bonds, each of which emerges as a combination of electrostatic, polarization, dispersion, and donor-acceptor or covalent interactions. In this work, ab initio molecular dynamics was tailored to isolate and switch off the covalent component of interactions between water molecules in simulations. Comparison of simulations with and without covalency shows that a small amount of intermolecular electron density transfer has a profound effect on the structure and dynamics of the hydrogen-bond network and thus on observable properties of room-temperature liquid water.

Low-Dimensional Confined Ice Has the Electronic Signature of Liquid Water

“…32−43 Although the quantitative contribution of the CT effect to the overall binding energy is computed differently in various theoretical approaches it is clear that, even with conservative estimates, donor−acceptor orbital interactions between molecules play an important role in physics and chemistry of bulk water. 44 Multiple studies 45−51 have pointed out a connection between the donor−acceptor interactions and measurable properties of bulk liquid water such as features of the X-ray absorption, infrared, and nuclear magnetic resonance spectra. It is therefore essential to perform a comparative analysis of donor−acceptor electronic interactions in bulk water and in extreme low-dimensional environments.…”

“…The absence of these interactions in the analytical force-field equation is instead compensated by the increased strength of the electrostatic and/or polarization interactions. 44 The compensating terms are traditionally tuned to reproduce properties of bulk water, not properties of low-dimensional confined water. While the structure of low-dimensional water obtained here with the SPC/E force field agrees well with the experimentally available data, comparative EDA demonstrates that, electronically, donor−acceptor interactions are different in bulk and confined ice and suggests that the missing CT interactions in confined water are improperly compensated in the commonly employed force fields.…”

CP2K: An Electronic Structure and Molecular Dynamics Software Package -- Quickstep: Efficient and Accurate Electronic Structure Calculations

“…Another unique feature of the implementation in CP2K is the ability to control the spatial range of charge-transfer between molecules using the cutoff radius R c of CLMOs (see Section VIII B). Additionally, the ALMO EDA in combination with CP2K's efficient AIMD engine allows to switch off the CT term in AIMD simulations, thus measuring the CT contribution to dynamical properties of molecular systems [289].…”

“…The ALMO EDA has been applied to study intermolecular interactions in a variety of gas-and condensed-phase molecular systems [288,290]. The CP2K implementation of ALMO EDA has been particularly advantageous to understand the nature of hydrogen bonding in bulk liquid water [208,214,216,255,258,259,261,289], ice [291] and water phases confined to low dimensions [292]. Multiple studies have pointed out a deep connection between the donor-acceptor interactions and features of the X-ray absorption [214,293], infrared (IR) [255,256,258,261,289,294,295] (Fig.…”

“…Extension of ALMO EDA to AIMD simulations have shown that the insignificant covalent component of HB determines many unique properties of liquid water including its structure (Fig. 8), dielectric constant, hydrogen bond lifetime, rate of self-diffusion and viscosity [210,289].…”