Molecular Dynamics Study of Homogeneous Nucleation in Supercooled Clusters of tert-Butyl Chloride. Transition from Tetragonal to Monoclinic Phase

Bartell, Lawrence S.; Chen, Jian

doi:10.1021/j100033a012

Cited by 9 publications

(7 citation statements)

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“…It is worth commenting that the curves in Figure 11 display irregularities, some more than others, in the vicinity of the transition from bcc to monoclinic. In some prior simulations 11 it had been observed that the greater compactness of the packing in the low-temperature phase created a tension in the phase surrounding it that tended to disrupt the outer structure. This course of events may help to account for the irregularities.…”

Section: Discussionmentioning

confidence: 99%

“…[9][10][11] If a realistic intermolecular interaction function can be constructed, it is possible to follow the molecular trajectories that lead to nucleation. Indeed, many MD investigations of phaselike changes in extremely small clusters of atoms have already been made, 12 and several have been carried out on clusters of polyatomic molecules.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, many MD investigations of phaselike changes in extremely small clusters of atoms have already been made, 12 and several have been carried out on clusters of polyatomic molecules. [9][10][11][13][14][15][16][17][18][19][20][21] Quite a few have also been performed on the freezing of bulk atomic systems. 22 As shown in a classic paper by Swope and Andersen, 22 however, artifacts arising from the imposition of periodic boundary conditions have distorted conclusions derived from most simulations of the freezing of bulk systems.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Study of the Freezing of Clusters of Chalcogen Hexafluorides

Kinney

Bartell

1996

J. Phys. Chem.

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Because knowledge about homogeneous nucleation in supercooled molecular liquids is largely indirect, a molecular dynamics investigation of the freezing of liquid clusters was initiated to furnish a plausible account of the molecular behavior involved. Results of the first stage of research are reported. Clusters with free boundaries were chosen instead of bulk systems in order to avoid the interference introduced by periodic boundary conditions. Systems of 150-molecule clusters of SF 6 , SeF 6 , and TeF 6 were examined. Analyses of Voronoi polyhedra in the warm systems prepared confirmed that the clusters were genuinely liquid, containing no crystalline seeds capable of initiating freezing. As the clusters cooled, random structural fluctuations created short-lived embryonic nuclei. At deeper supercooling, a nucleus of critical size ultimately appeared in each cluster and freezing began. When cooled at a rate of 2 × 10 10 K/s or more slowly, all clusters froze to bcc single crystals and these transformed to monoclinic single crystals upon further cooling. Voronoi polyhedra gave much more delicate and definitive analyses of the presence of solid nuclei than did other common indices such as the Lindemann δ. The polyhedra, however, were quite blind to the solid-state transition to monoclinic. It was found that the threshold value of the Lindemann index for freezing decreased systematically with increasing size of the molecules. The reported failure of similar systems to freeze in prior molecular dynamics simulations may have been due to the faster cooling rates adopted.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Study of the Freezing of Clusters of Chalcogen Hexafluorides

Kinney

Bartell

1996

J. Phys. Chem.

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“…With the advent of desktop workstations that are faster than yesterday's supercomputers, it is now feasible to examine details of nucleation that have previously been obscure. The systems studied in most previous simulations of nucleation in condensed phases have been freezing atomic liquids, − although a few studies of polyatomic systems undergoing freezing − or solid-state transitions in small clusters at deep supercooling have been reported. The present investigation follows up several of these.…”

Section: Introductionmentioning

confidence: 99%

Freezing of Small SeF₆ Clusters: Simulations, Nucleation Statistics When Events Are Few, and Effects of Laplace Pressure

1999

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Simulations were carried out on 138-molecule clusters freezing isothermally at 130, 120, and 80 K. At 120 K, the nucleation rate was the same as in our prior simulations performed adiabatically but the final product was different. During the nanosecond period of the runs, clusters transforming adiabatically had frozen to bcc crystals while warming from 120 K to about 130 K. On the other hand, isothermal clusters at 120 and 130 K changed to monoclinic clusters after passing through the bcc phase. Clusters cooled to 80 K froze to a variety of structures. The number of molecules whose Voronoi polyhedra qualified them as being in bcc embryos grew in size erratically, and in most runs it was difficult to use the Voronoi information by itself to identify a well-characterized nucleation time. Therefore, a more discriminating criterion for the onset of nucleation was devised. The 138-molecule clusters proved to be too small to yield definitive profiles of the several order parameters characterizing the change from the liquid phase to the critical nucleus. Even though the sizes of the nuclei were not established accurately, it was clear that critical nuclei were considerably larger than the five-molecule size forecast by the classical theory of homogeneous nucleation. At the deep supercooling of the simulations, precritical and critical nuclei were extremely ramified and haphazard in molecular orientation, but the chaotically organized nuclei at 120 and 130 K quickly annealed and grew to single crystals in most clusters. Clues were found suggesting that surface molecules may participate in the formation of critical nuclei, contrary to our long-standing belief. From nucleation rates were derived the kinetic parameters σsl, the solid−liquid interfacial free energy of the classical nucleation theory, and δ, the interface thickness of Gránásy's diffuse interface theory (DIT). In addition, the effect of pressure on the DIT, a new treatment of errors, and an improved weighted least-squares analysis of nucleation data were developed.

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“…A variety of solid state and freezing transitions have been observed in large molecular clusters as they cool in supersonic flow . Several of these transitions have also been seen to occur spontaneously in molecular dynamics (MD) simulations of cooling clusters. − Clusters are particularly convenient systems for MD simulations of phase transitions because clusters avoid the severe limitations imposed by periodic boundary conditions. In both the experimental and computational research it is possible to determine rates of genuinely homogeneous nucleation, a notoriously difficult phenomenon to achieve, verify, and characterize by more conventional techniques.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Study of a Crystalline Cluster Undergoing a Second-Order Transition. An Inchoate Model of Acetylene

Santikary

Bartell

1997

J. Phys. Chem. A

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To extend our molecular dynamics studies of nucleation in molecular clusters undergoing phase changes, we selected the acetylene system whose clusters had already been examined experimentally in supersonic flow. Because molecular dynamics simulations based on the several existing model potential functions were incapable of accounting for the structure of the low-temperature orthorhombic phase, a new interaction potential was developed which successfully yielded the correct molecular packing at low temperatures as well as the cubic structure observed at high temperatures. The results obtained in heating and cooling runs for the model system were unlike any seen in our prior simulations. There was no nucleation barrier inhibiting the passage from the cubic to the orthorhombic phase on cooling, nor were there discernible volume or enthalpy changes in the transformation. In clusters of several hundred molecules the apparently second-order or continuous transition was spread over a much wider range of temperatures than had been seen in first-order transitions in previous simulations. Although the results provide an instructive example of an unusual type of transformation, they do not appear to correspond to the transition observed experimentally for pure, bulk acetylene.

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Molecular Dynamics Study of Homogeneous Nucleation in Supercooled Clusters of tert-Butyl Chloride. Transition from Tetragonal to Monoclinic Phase

Cited by 9 publications

References 10 publications

Molecular Dynamics Study of the Freezing of Clusters of Chalcogen Hexafluorides

Molecular Dynamics Study of the Freezing of Clusters of Chalcogen Hexafluorides

Freezing of Small SeF₆ Clusters: Simulations, Nucleation Statistics When Events Are Few, and Effects of Laplace Pressure

Molecular Dynamics Study of a Crystalline Cluster Undergoing a Second-Order Transition. An Inchoate Model of Acetylene

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Molecular Dynamics Study of Homogeneous Nucleation in Supercooled Clusters of tert-Butyl Chloride. Transition from Tetragonal to Monoclinic Phase

Cited by 9 publications

References 10 publications

Molecular Dynamics Study of the Freezing of Clusters of Chalcogen Hexafluorides

Molecular Dynamics Study of the Freezing of Clusters of Chalcogen Hexafluorides

Freezing of Small SeF6 Clusters: Simulations, Nucleation Statistics When Events Are Few, and Effects of Laplace Pressure

Molecular Dynamics Study of a Crystalline Cluster Undergoing a Second-Order Transition. An Inchoate Model of Acetylene

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Freezing of Small SeF₆ Clusters: Simulations, Nucleation Statistics When Events Are Few, and Effects of Laplace Pressure