Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211-7600, USA.
J Chem Phys. 2010 Nov 21;133(19):194501. doi: 10.1063/1.3504610.
The crystallization of nitromethane, CH(3)NO(2), from the melt on the (100), (010), (001), and (110) crystal surfaces at 170, 180, 190, 200, 210, and 220 K has been investigated using constant-volume and -temperature (NVT) molecular dynamics simulations with a realistic, fully flexible force field [D. C. Sorescu, B. M. Rice, and D. L. Thompson, J. Phys. Chem. B 104, 8406 (2000)]. The crystallization process and the nature of the solid-liquid interface have been investigated by computing the molecular orientations, density, and radial distribution functions as functions of time and location in the simulation cell. During crystallization the translational motion of the molecules ceases first, after which molecular rotation ceases as the molecules assume proper orientations in the crystal lattice. The methyl groups are hindered rotors in the liquid; hindrance to rotation is reduced upon crystallization. The width of the solid-liquid interface varies between 6 and 13 Å (about two to five molecular layers) depending on which crystal surface is exposed to the melt and which order parameter is used to define the interface. The maximum rate of crystallization varies from 0.08 molecules ns(-1) Å(-2) for the (010) surface at 190 K to 0.41 molecules ns(-1) Å(-2) for the (001) surface at 220 K.
硝甲烷（CH(3)NO(2)）在 170、180、190、200、210 和 220 K 时从熔体在（100）、（010）、（001）和（110）晶体表面结晶的过程已通过使用真实、完全灵活的力场的定容和定温（NVT）分子动力学模拟进行了研究[D. C. Sorescu、B. M. Rice 和 D. L. Thompson，J. Phys. Chem. B 104，8406（2000）]。通过计算分子取向、密度和径向分布函数随时间和模拟单元中位置的函数，研究了结晶过程和固液界面的性质。在结晶过程中，分子的平移运动首先停止，然后分子旋转停止，因为分子在晶格中采用适当的取向。在液体中，甲基基团是受阻转子；结晶时旋转受阻减少。固液界面的宽度在 6 到 13 Å 之间变化（约两到五个分子层），具体取决于暴露于熔体的晶体表面和用于定义界面的哪个序参量。结晶的最大速率从 190 K 时（010）表面的 0.08 个分子 ns(-1) Å(-2)到 220 K 时（001）表面的 0.41 个分子 ns(-1) Å(-2)变化。
