富勒烯的相变：Fragmentation和碳笼的重组
Phase transitions in fullerenes: Fragmentation and reassembly of the carbon cage
摘要：
用恒温分子动力学模拟研究了富勒烯C60和C240的相变。在相变区域，通过两相的动力学共存，证明了C60笼从（和到）气态的组装（和碎裂）。在这个关键区域，富勒烯系统在碳笼（固相）与碳二聚体和短链状态（气相）之间连续振荡。这些振荡对应于富勒烯的连续分解和形成。此外，温度依赖的热容量的富勒烯功能的一个突出的峰值，表示有限系统模拟的一阶相变。使用为这项工作开发的拓扑约束成对力场进行了500 ns的模拟。模拟结果补充了统计力学分析，以解释熵和压力校正，对应于实验条件。这些修正导致的相变温度为3800-4200 K的压力为10-100 kPa，与现有的实验值符合良好。
英文摘要：
Phase transition in fullerenes C60 and C240 are investigated by means of constant-temperature molecular dynamics simulations. In the phase transition region, the assembly (and fragmentation) of the C60 cage from (and to) the gaseous state is demonstrated via the dynamical coexistence of two phases. In this critical region, the fullerene system is seen to continuously oscillate between the carbon cage (the solid phase) and the state of carbon dimers and short chains (the gas phase). These oscillations correspond to consecutive disintegration and formation of the fullerene. Furthermore, the temperature-dependent heat capacity of the fullerene features a prominent peak, signifying the finite system analogue of a first-order phase transition. The simulations were conducted for 500 ns using a topologically-constrained pairwise forcefield which was developed for this work. Results of the simulations were supplemented by a statistical mechanics analysis to account for entropy and pressure corrections, corresponding to experimental conditions. These corrections lead to a phase transition temperature of 3800-4200 K for pressure 10-100 kPa, in good agreement with available experimental values.
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