Simulations of the methane hydrate/methane gas interface near hydrate forming conditions conditions

Rodger, P. Mark; Forester, Timothy R.; Smith, William R.

doi:10.1016/0378-3812(95)02903-6

Cited by 215 publications

(184 citation statements)

References 11 publications

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“…If the energetic cost to further reduce the water content is higher than that of transforming it into an sII nucleus, the second process will prevail. To analyze how the framework formed by water molecules in the nucleus changes along the NP, we measure the F 4 order parameter 47 of H 2 O molecules belonging to the nucleus at the five points of Figure 3. values, with a ∼25% difference between the most (60°, 180°, and 300°) and least (0, 120°, and 240°) probable angles.…”

Section: Resultsmentioning

confidence: 99%

Methane Clathrate Hydrate Nucleation Mechanism by Advanced Molecular Simulations

et al. 2014

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The nucleation mechanisms of methane hydrates are studied using welltempered metadynamics and restrained molecular dynamics. The collective variables we used to follow the process are the methane−methane and methane−water coordination numbers, from which we computed the corresponding Landau free energy surface. This surface is characterized by two minima, corresponding to the two-phase methane bubble/ water solution and clathrate crystal, and a transition state. The clathrate crystal is of type II, while in the simulation conditions (T = 273 K and P = 500 atm) the most stable phase should be type I. We constructed the steepest ascent/descent path connecting the twophase methane bubble/water solution to the clathrate state and passing through the transition state. We interpret this path as the nucleation path, which shows four phases. First, the concentration of solvated methane increases in the aqueous domain via diffusion through the methane−water interface. Second, units of methane molecules solvated in water meet to form an unstructured cluster. Third, the water content of the nucleus decreases to a value compatible with the type II methane clathrate hydrate composition. Finally, a reordering process of solvated methane and water molecules occurs in a manner consistent with the "blob" hypothesis (Jacobson, L. C.; Hujo, W.; Molinero, V.

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Section: Resultsmentioning

confidence: 99%

Methane Clathrate Hydrate Nucleation Mechanism by Advanced Molecular Simulations

et al. 2014

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“…5,28,29 Radhakrishnan and Trout defined a further order parameter based on the number of guests at a suitable distance from the central one, i.e., within the domain of the first peak of the guest-guest pair correlation function of hydrates. 4 Further, geometric hydrate-liquid recognition criteria have focussed on identification of hydrate-like cavities, either polyhedral (i.e., 5 12 , 5 12 6 2 , 5 12 6 3 , or 5 12 6 4 ) 10,16,30,31 or halfpolyhedral (i.e., 5 6 , 5 6 6 1 , or 5 6 6 2 ).…”

Section: Introductionmentioning

confidence: 99%

Clathrate structure-type recognition: Application to hydrate nucleation and crystallisation

Lauricella

Meloni

Liang

et al. 2015

The Journal of Chemical Physics

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For clathrate-hydrate polymorphic structure-type (sI versus sII), geometric recognition criteria have been developed and validated. These are applied to the study of the rich interplay and development of both sI and sII motifs in a variety of hydrate-nucleation events for methane and H2S hydrate studied by direct and enhanced-sampling molecular dynamics (MD) simulations. In the case of nucleation of methane hydrate from enhanced-sampling simulation, we notice that already at the transition state, ∼80% of the enclathrated CH4 molecules are contained in a well-structured (sII) clathrate-like crystallite. For direct MD simulation of nucleation of H2S hydrate, some sI/sII polymorphic diversity was encountered, and it was found that a realistic dissipation of the nucleation energy (in view of non-equilibrium relaxation to either microcanonical (NVE) or isothermal-isobaric (NPT) distributions) is important to determine the relative propensity to form sI versus sII motifs.

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“…During hydrate nucleation, a system's potential energy decreases with approximately concurrent increases in both: (i) the number of water cages in the system, and (ii) system order according to molecular-level, water-based order parameters [e.g., the F 4 order parameter (22)]. This can be seen by comparing the time evolution of these properties for one of this study's trajectories (e.g., see run 2 in Fig.…”

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confidence: 99%

Evidence from mixed hydrate nucleation for a funnel model of crystallization

Hall

Carpendale

Kusalik

2016

Proc. Natl. Acad. Sci. U.S.A.

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The molecular-level details of crystallization remain unclear for many systems. Previous work has speculated on the phenomenological similarities between molecular crystallization and protein folding. Here we demonstrate that molecular crystallization can involve funnel-shaped potential energy landscapes through a detailed analysis of mixed gas hydrate nucleation, a prototypical multicomponent crystallization process. Through this, we contribute both: (i) a powerful conceptual framework for exploring and rationalizing molecular crystallization, and (ii) an explanation of phenomenological similarities between protein folding and crystallization. Such funnel-shaped potential energy landscapes may be typical of broad classes of molecular ordering processes, and can provide a new perspective for both studying and understanding these processes. nucleation | gas clathrate hydrates | potential energy landscapes | crystallization funnel | molecular dynamics simulation M olecular crystallization and its inhibition are important to a broad range of fields. For example, some organisms [such as Antarctic fish (1) and winter rye (2)] have developed a rich chemistry of antifreeze proteins to control internal freezing, and there is significant interest in exploiting antifreeze proteins for food applications (e.g., see ref.3). Gas hydrate formation in oil and gas pipelines is a major industrial concern (4). For pharmaceuticals, there is much interest in understanding and controlling crystal polymorphism (e.g., see ref. 5). A better understanding of molecular crystallization, and factors influencing these processes, has potential to aid further advancements in such fields. As highlighted by a recent review on crystallization (6), traditional theoretical models of crystallization (e.g., classical nucleation theory) have proven to be problematic for a variety of systems and there remain technical challenges to studying crystallization both experimentally and computationally, so a clear understanding of crystal nucleation has yet to emerge.Molecular crystallization is one of the major classes of molecular ordering processes. Other molecular ordering processes include micelle formation, the formation of coordination polymers, and protein folding. Previous work has asserted, although not substantiated, that crystallization and protein folding are somehow similar processes. For example, protein folding has been speculatively described as a first-order phase transition similar to liquidsolid transitions (7). It has also been proposed that both the waterice transition and protein folding are difficult to study in silico because both are complex searches for relatively few ordered structures among numerous disordered alternative structures (8). The aim of this study is twofold: (i) to provide a conceptual description of molecular crystallization (simply referred to as crystallization henceforth), and (ii) to provide an explanation of the apparent similarities between crystallization and protein folding. On the basis of extensive simulati...

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Simulations of the methane hydrate/methane gas interface near hydrate forming conditions conditions

Cited by 215 publications

References 11 publications

Methane Clathrate Hydrate Nucleation Mechanism by Advanced Molecular Simulations

Methane Clathrate Hydrate Nucleation Mechanism by Advanced Molecular Simulations

Clathrate structure-type recognition: Application to hydrate nucleation and crystallisation

Evidence from mixed hydrate nucleation for a funnel model of crystallization

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