Journal
MOLECULAR SIMULATION
Volume 45, Issue 18, Pages 1524-1537Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/08927022.2019.1660326
Keywords
Density functional theory; sH hydrate; compressional anisotropy; isothermal bulk modulus; hydrogen bond density
Funding
- Natural Sciences and Engineering Research Council (NSERC) [42069]
- Calcul Quebec
- Compute Canada [CCRI: xvj-290-01]
- McGill Engineering Doctoral Awards (MEDA McGill Scholarship)
- James McGill Professorship appointment [00152]
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Structure-H (sH) hydrate is one of the canonical gas hydrates with significant potential applications and scarce characterised material properties despite the wide knowledge available on other gas hydrates. In this work we characterise some of the important physical properties of this hydrate at the atomistic level using Density Functional Theory. Two exchange-correlation functionals (revPBE and DRSLL) were used to simulate six sH hydrate systems encapsulating neohexane and different help gas molecules. The important role of dispersion forces is quantified. The density and isothermal bulk modulus of sH hydrate are higher when dispersion interactions are considered. The presence of those interactions imposes a direct relationship between the hydrate density and its bulk modulus, while their absence reveals the bulk modulus dependency on hydrogen bond density. Anisotropy is a distinguishing feature of this hydrate in distinction to nearly isotropic sI and sII hydrates. Structure-H hydrate experiences a compressional anisotropy in which the a-lattice and the c-lattice constants respond differently to applied pressure showing less compressibility along the c-axis. This compressional anisotropy was found dependant on the chemistry of help gas molecules. Taken together, these property characterisation results and analysis are a significant and novel contribution to the material physics of sH hydrates.
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