Phase behaviour of the quantum Lennard-Jones solid

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. This dataset contains input files and run scripts for the quasiharmonic calculations using GULP, and the PIMD calculations using i-PI and LAMMPS. See README.txt files within each archive for specific details on how to run and analyze the calculations.

伦纳德-琼斯势（Lennard-Jones potential）或许是应用最为广泛的不带电粒子（如稀有气体固体）相互作用模型之一。经典伦纳德-琼斯固体的相图已被证实存在六方最密堆积（hexagonal close-packed, hcp）与面心立方（face-centered cubic, fcc）相之间的结构转变。然而，量子版伦纳德-琼斯固体的相行为仍未明确。本研究采用基于路径积分分子动力学（path integral molecular dynamics, PIMD）与晶格动力学计算的热力学积分方法，探究了hcp与fcc型伦纳德-琼斯固体的相稳定性。研究发现，在PIMD模拟中量子效应可稳定hcp相，而晶格动力学计算则表明fcc相更具优势，这意味着对于强量子体系，可能存在低压下的复现hcp相。本文还讨论了该研究对稀有气体固体相稳定性研究的启示。当参数对应氦元素时，由零点振动引发的晶格膨胀与量子熔化现象相关联：此时两种晶体结构在零压下均无法稳定存在。本数据集包含使用GULP软件开展准谐近似计算的输入文件与运行脚本，以及使用i-PI和LAMMPS软件进行PIMD计算的相关文件。每个压缩包内的README.txt文件均包含计算运行与分析的具体操作细节。