Thermal properties of gas hydrates and their underlying fundamental characterization are limited and incomplete but crucial in ongoing basic science research and technological applications. The constant volume heat capacity, the constant pressure heat capacity, the volumetric thermal expansion coefficient, and the Grüneisen parameter of methane, ethane, ethylene oxide, carbon dioxide, and empty structure I hydrates, and of hexagonal ice, as functions of temperature from 0 to 300 K, were calculated using the integration of density functional theory (DFT) simulations at 0 K and phonon calculations at higher temperatures. At low temperatures, DFT predictions replicated experimental values of constant pressure heat capacity for hydrates and ice accurately. Notably, the constant volume heat capacity was lower than when compared with literature values calculated with molecular dynamics (MD) and closer to actual data. Guest molecules were found to contribute slightly more than their ideal gas heat capacities to the overall property of the system. DFT underestimated the thermal expansion coefficient in all cases. The ethane and carbon dioxide hydrates demonstrated behavior that was markedly different when compared to methane and empty hydrates, and hexagonal ice. The Grüneisen parameter was calculated for all systems. DFT overestimated the value of the parameter for filled hydrates and hexagonal ice when compared to experimental hexagonal ice values. Altogether, this systematic atomistic study contributes to the technological applications and basic material science of these crystals whose properties are of significant importance in the fields of energy and the environment and provides a potential input to MD simulations thanks to its performance at low temperatures.

(1) Background: New technologies involving gas hydrates under pre-nucleation conditions such as gas separations and storage have become more prominent. This has necessitated the characterization and modeling of the transport properties of such systems. (2) Methodology: This work explored methane hydrate systems under pre-nucleation conditions. All-atom molecular dynamics simulations were used to quantify the performance of the TIP4P/2005 and TIP4P/Ice water models to predict the viscosity, diffusivity, and thermal conductivity using various formulations. (3) Results: Molecular simulation equilibrium was robustly demonstrated using various measures. The Green–Kubo estimation of viscosity outperformed other formulations when combined with TIP4P/Ice, and the same combination outperformed all TIP4P/2005 formulations. The Green–Kubo TIP4P/Ice estimation of viscosity overestimates (by 84% on average) the viscosity of methane hydrate systems under pre-nucleation conditions across all pressures considered (0–5 MPag). The presence of methane was found to increase the average number of hydrogen bonds over time (6.7–7.8%). TIP4P/Ice methane systems were also found to have 16–19% longer hydrogen bond lifetimes over pure water systems. (4) Conclusion: An inherent limitation in the current water force field for its application in the context of transport properties estimations for methane gas hydrate systems. A re-parametrization of the current force field is suggested as a starting point. Until then, this work may serve as a characterization of the deviance in viscosity prediction.

Gas hydrates are inclusion compounds of a water backbone that encloses gaseous molecules. Thanks to their applications in gas recovery, carbon capture and storage, gas storage, and flow assurance, generating high quality data and predictions of their properties is paramount. A review of novel techniques using first principles density functional theory and molecular dynamics simulations methods coupled to auxiliary simulations methods is presented herein.Structure I (sI), structure II (sII), and structure H (sH) hydrates have been studied extensively, with studies of their material strength showing that it is often misleading to use the properties of ice instead of the difficult-todetermine gas hydrate properties. Key differences between the three structures and their possible guests are presented. The interfacial properties of gas hydrates display key behaviours that control nucleation and growth, which are important phases in controlling and monitoring their formation. Gas hydrate thermal properties are also examined, with key differences existing between guests and some unusual alignment in the cages shown for carbon dioxide, ethane, and ethylene oxide sI hydrates. First principles infrared spectroscopy is also examined, with techniques showing that these signatures can be tied to and predict material properties to improve the speed of analysis. Therefore, by quantifying, modelling, predicting, and explaining their formation and dissociation, and linking these to their thermal, material, and interfacial properties, a database of reliable data for science and engineering methods and applications is formed to provide a basis for further work.

(1) Background: Gas hydrates are historically notable due to their prevalence and influence on operational difficulties in the oil and gas industry. Recently, new technologies involving the formation of gas hydrates to accomplish various applications have been proposed. This has created new motivation for the characterization of rheological and mechanical properties and the study of molecular phenomena in gas hydrates systems, particularly in the absence of oil and under pre-nucleation conditions. (2) Methodology: This work reviews advances in research on the promotion, inhibition, rheology, and mechanical properties of gas hydrates obtained through an integrated material synthesis-property characterization-multi-scale theoretical and computational platform at McGill University. (3) Discussion: This work highlights the findings from previous experimental work by our group and identifies some of their inherent physical limitations. The role of computational research methods in extending experimental results and observations in the context of mechanical properties of gas hydrates is presented. (4) Summary and Future perspective: Experimental limitations due to the length and time scales of physical phenomena associated with gas hydrates were identified, and future steps implementing the integrated experimental-computational platform to address the limitations presented here were outlined.

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