The processes of nucleation and growth of methane hydrate in a highly supercooled two-phase methane–water system obtained using various cooling protocols are considered. It has been shown that, at sufficiently high cooling rates, crystalline forms of methane hydrate can still form in the system. It was found that, at a cooling rate of γ = 1.0 K/ps, the process of nucleation and growth of gas hydrate was observed in all independent molecular dynamics iterations, while at a cooling rate of γ = 10.0 K/ps, no nucleation event was observed in ~26.7% of numerical experiments. It was found that with an increase in the cooling rate of the system, an increase in the average time scale of nucleation τc and a decrease in the critical size of the nucleus nc are observed. It is shown that at a sufficiently deep level of supercooling of the system, the scenario of homogeneous crystalline nucleation is realized at the initial stage of the phase transition.
Glass formation processes in condensed matter are characterized by some specific short-range order changes in the arrangement of particles (atoms/molecules/ions). So, the short-range structural order in supercooled liquids and glasses is characterized by fivefold symmetry in the arrangement of particles, often referred to as icosahedral (ideal or distorted) short-range order. This article is devoted to the study of local structural features of the supercooled melt of the A20B80 fullerene mixture (where A = C60 and B = C70) obtained under various cooling protocols in order to elucidate the mechanism of formation of the icosahedral short-range order in binary molecular liquids. Comprehensive studies of the properties of a fullerene mixture melt were carried out using large-scale molecular dynamics simulations followed by structural and cluster analysis. The crystallization temperature and the critical glass transition temperature of the system were calculated to be Tm ≈ 1439 K and Tc ≈ 1238 K, respectively. It has been established that the crystallization of a binary fullerene mixture proceeds according to the polycrystalline scenario with the formation of clusters with fcc and hcp symmetries. It is shown that in a supercooled fullerene mixture, the short-range icosahedral order is formed by an insignificant number of ideal icosahedral clusters and a certain set of distorted icosahedral clusters, the fraction of which remains practically unchanged at temperatures below the critical glass transition temperature.
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