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arXiv 2006.07672cond-mat.mtrl-sciphysics.comp-phquant-ph
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量子Lennard-Jones固体的相行为

Phase behaviour of the quantum Lennard-Jones solid

Heather Wiebe, Tom L. Underwood, Graeme J. Ackland

摘要:

Lennard-Jones势可能是不带电粒子(如惰性气体固体)相互作用的最广泛使用的模型之一。已知经典LJ固体的相图显示hcp和fcc相之间的转变。然而,量子Lennard-Jones固体的相行为仍然未知。采用基于路径积分的热力学积分分子动力学和晶格动力学计算方法研究了六方晶系和面心立方晶系Lennard-Jones固体的相稳定性。HCP相被证明是稳定的PIMD的量子效应,而fcc被证明是有利于晶格动力学,这表明一个可能的重入低压HCP相的高量子系统。惰性气体固体的相稳定性的影响进行了讨论。对于等同于氦的参数,由于零点振动引起的膨胀与量子熔化有关:在零压力下,两种晶体结构都不稳定。

英文摘要:

The Lennard-Jones potential is perhaps one of the most widely-used models for the interaction of uncharged particles, such as noble gas solids. The phase diagram of the classical LJ solid is known to exhibit transitions between hcp and fcc phases. However, the phase behaviour of the quantum Lennard-Jones solid remains unknown. Thermodynamic integration based on path integral molecular dynamics and lattice dynamics calculations are used to study the phase stability of the hcp and fcc Lennard-Jones solids. The hcp phase is shown to be stabilized by quantum effects in PIMD while fcc is shown to be favoured by lattice dynamics, which suggests a possible re-entrant low pressure hcp phase for highly quantum systems. Implications for the phase stability of noble gas solids are discussed. For parameters equating to Helium, the expansion due to zero-point vibrations is associated with quantum melting: neither crystal structure is stable at zero pressure.

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