Water dynamics: Relation between hydrogen bond bifurcations, molecular jumps, local density & hydrophobicity

TL;DR

This study uses ab initio molecular dynamics to explore water's structure and dynamics, revealing how hydrogen bond bifurcations, molecular jumps, local density, and hydrophobicity are interconnected at femtosecond timescales.

Contribution

It demonstrates the fundamental coupling between large-angle jumps, bond bifurcations, and local density fluctuations in water, advancing understanding of water's microscopic behavior.

Findings

Large-angle jumps and bond bifurcations are fundamental to water dynamics.

Local density differences drive bond bifurcations and molecular jumps.

Water rotation is facilitated by the negativity track from oxygen lone pairs.

Abstract

Structure and dynamics of water remain a challenge. Resolving the properties of hydrogen bonding lies at the heart of this puzzle. Here we employ ab initio Molecular Dynamics (AIMD) simulations over a wide temperature range. The total simulation time was approx 2 ns. Both bulk water and water in the presence of a small hydrophobic molecule were simulated. We show that large-angle jumps and bond bifurcations are fundamental properties of water dynamics and that they are intimately coupled to both local density and hydrogen bond stretch oscillations in scales from about 60 to a few hundred femtoseconds: Local density differences are the driving force for bond bifurcations and the consequent large-angle jumps. The jumps are intimately connected to the recently predicted energy asymmetry. Our analysis also appears to confirm the existence of the so-called negativity track provided by the lone pairs of electrons on the oxygen atom to enable water rotation.