Intra-Cage Structure, Vibrations and Tetrahedral-Site Hopping of H2 and D2 in Doubly-Occupied 51264 Cages in sII Clathrate Hydrates from Path-Integral and Classical Molecular Dynamics

Niall J English,Christian J Burnham

doi:10.3390/app11010054

Abstract

The intra-cage behaviour of guest H2 and D2 molecules in doubly occupied 51264 cages in structure-II (sII) clathrate hydrates were investigated using classical and path-integral molecular dynamics at 100 K. We probed the structure of tetrahedral sites, proton vibrations, localised molecular rattling timescales at sites, and the jump-diffusion travel of H2 and D2 molecules between sites. The site-diffusion model was correlated with experimental neutron scattering data, and the cage occupancies were then discussed in light of recent state-of-the-art experimental and theoretical findings in the literature.

Highlights

Hydrogen is considered to be the ultimate alternative clean fuel to supplant the use of hydrocarbons in many contexts
The model was parameterised against Born-Oppenheimer molecular dynamics (BOMD) trajectories of type II clathrate hydrates containing guest hydrogen molecules
Turning to the matter of investigating the so-defined and resultant tetrahedral sites in terms of their hopping dynamics and distribution of dwell times therein, we identified every doubly occupied large cage in our simulation cell, recording the labels of the molecules forming the vertices of each cage

Summary

Introduction

Hydrogen is considered to be the ultimate alternative clean fuel to supplant the use of hydrocarbons in many contexts. We sought to investigate further tetrahedral-site distributions for doubly occupied large cages using path-integral dynamics to incorporate nuclear quantum effects at 100 K.

Results

Conclusion