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Radial distribution functions (a) СO 2 -CO 2 (C-C) and (b) СO 2 -H 2 O (C-O) under isobaric conditions at different temperatures: (1) 210, (2) 220, and (3) 230 K.

Radial distribution functions (a) СO 2 -CO 2 (C-C) and (b) СO 2 -H 2 O (C-O) under isobaric conditions at different temperatures: (1) 210, (2) 220, and (3) 230 K.

Contexts in source publication

Context 1
... isochoric conditions, the peaks in the RDF of the gas molecules (C-C) began to be smeared already at 200 K, while the complete destruction was observed at 220 K. Fot the simulation of carbon dioxide hydrate under the isobaric conditions, the crystalline structure disappeared in the C-C distribution function at 230 K irrespective of the pressure (Fig. 3a). As in the case of methane hydrate, the number of adja-cent gas molecules was equal to nine and close to zero (0.3 at 230 K) before and after melting, ...
Context 2
... is seen in Fig. 3, CO 2 melts more abruptly than does CH 4 hydrate. This finding is confirmed by the fact that the numbers of adjacent neighbors at premelting temperatures are larger in the case of carbon dioxide: 8 gas molecules and 15 water molecules at 230 K, while, for methane, they are 5 and 7 molecules, respectively, at 260 ...
Context 3
... conditions, a noticeable increase in the diffusion coefficient of H 2 O takes place already at 230-240 K, while for methane, it is observed at 250 K (Fig. 4, curves 2, 4). When simulating the system at a constant pressure of 50 atm, the mobility of molecules begins to increase at higher temperatures: 240-250 K for water and 260 K for methane (Fig. 4, curves 1, 3). Judging by the data obtained, it may be assumed that methane hydrate begins to melt at 250 and 260 K under the isochoric and isobaric conditions, ...
Context 4
... coefficients of carbon dioxide at different temperatures are presented in Fig. 5. Mobility of gas molecules increases at temperatures of 220 and 230 K at constant volume and pressure, respectively (Fig. 5, curves 1, 3). For carbon dioxide hydrate at a constant pressure, additional calculations of melting were performed for a structure with incomplete filling, when only 86% of the cavities in the hydrate were initially occupied with the gas (Fig. 5, curve 2). It is seen that, below 230 K, the mobility of carbon dioxide molecules in the hydrate is ...
Context 5
... the intermolecular interaction weakens, while the potential energy increases. Before and after the range of melting, the E(T) dependences exhibit plateaus that correspond to the energies of the interaction between gas molecules in the hydrate and the aqueous solution, respectively. The melting of methane hydrate at a constant volume or pressure (Fig. 6, curves 1, 3) is accompanied by a dramatic increase in the potential energy at the same temperature (250 K). However, the plateau is reached (the melting is completed) under the conditions of a constant volume at a temperature (260 K) 10 K lower than it is at a constant pressure (270 ...
Context 6
... range that corresponds to melting appears to be markedly narrower than that for methane, as was noted above when analyzing the RDFs. Under the isochoric conditions, carbon dioxide hydrate begins to melt at 210 K (Fig. 6, curve 4), while the potential energy of the CO 2 -CO 2 interaction reaches the plateau at 220 K. In the NPT ensemble (Fig. 6, curve 3), no transition temperature range is observed, in which the hydrate has already begun to degrade but has not yet been decomposed completely; i.e., the CO 2 hydrate melts completely at 230 ...

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... Also, between different ensembles, the sequence of accurate clathrate nucleation was found to be NPT > NVT > NVE; however, the crystallinity sequence is exactly reversed [116]. According to the dissociation of CO 2 and CH 4 hydrates at 180-280 K, it was concluded that hydrate stability using isochoric conditions is lower than that in isobaric conditions [117]. Although remarkable advances in macroscopic measurements have been accomplished, MD simulations as a powerful technique can provide insights into the fundamental mechanisms of gas hydrates at molecular and atomistic levels. ...
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