Zero-point fluctuation of hydrogen bond in water dimer from ab initio molecular dynamics*

Abstract

Dynamic nature of hydrogen bond (H-bond) is central in molecular science of substance transportation, energy transfer, and phase transition in H-bonding networks diversely expressed as solution, crystal, and interfacial systems, thus attracting the state-of-the-art revealing of its phenomenological edges and sophisticated causes. However, the current understanding of the ground-state fluctuation from zero-point vibration (ZPV) lacks a firm quasi-classical base, concerning three basic dimensions as geometry, electronic structure, and interaction energy. Here, based on the ab initio molecular dynamics simulation of a ground-state water dimer, temporally separated fluctuation features in the elementary H-bond as the long-time weakening and the minor short-time strengthening are respectively assigned to two low-frequency intermolecular ZPV modes and two O–H stretching ones. Geometrically, the former modes instantaneously lengthen H-bond up to 0.2 Å whose time-averaged effect coverages to about 0.03 Å over 1-picosecond. Electronic-structure fluctuation crosses criteria’ borders, dividing into partially covalent and noncovalent H-bonding established for equilibrium models, with a 370% amplitude and the district trend in interaction energy fluctuation compared with conventional dragging models using frozen monomers. Extended physical picture within the normal-mode disclosure further approaches to the dynamic nature of H-bond and better supports the upper-building explorations towards ultrafast and mode-specific manipulation.

Hydrogen diffusion in C1′ phase clathrate hydrate

“…Those pioneering works indicate the important implications of efficient H 2 -storage by H 2 O-based crystals, however, the fundamental knowledge such as detailed diffusion mechanism in dense H 2 O-based crystals has not been wellunderstood. In this work, the diffusion behaviors of H 2 molecule in recently experimentally-synthesized C 1 clathrate hydrate [41] are explored using classic MD simulations, [49][50][51][52][53][54][55][56][57][58] focusing on the effects of cage occupancy, [59][60][61][62] as well as the free-energy landscapes. The outcomes of this study provide important insights into the diffusion of H 2 in C 1 phase clathrate hydrate, which is of help for H 2 gas purification, storage and transport by water-based clathrate structures.…”