Computational study of the interplay between intermolecular interactions and CO₂ orientations in type I hydrates

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Carbon dioxide (CO2) molecules enclathrated in type I hydrates display complex orientation patterns.
• Previous experimental and theoretical studies have partially explained these preferential CO2 orientations.

Purpose of the Study:

• To advance the theoretical understanding of CO2 orientations within type I hydrate structures.
• To investigate the roles of cavity geometry and intermolecular interactions in determining CO2 guest molecule behavior.

Main Methods:

• Classical molecular dynamics simulations.
• Electronic density functional theory calculations.

Main Results:

• Simulation results align with existing experimental and theoretical data on CO2 orientations.
• Steric constraints imposed by hydrate cavity geometry explain some, but not all, observed preferential angles.
• Guest-molecule interactions between neighboring cages are crucial for explaining the remaining experimental orientations.

Conclusions:

• Both steric effects and guest-guest interactions are key factors governing CO2 orientation in type I hydrates.
• The influence of guest-guest interactions on hydrate properties necessitates their inclusion in equation of state modeling.
• Current practices neglecting guest-guest interactions in hydrate modeling may require revision.