Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstr. 6, D-53115 Bonn, Germany.
J Chem Phys. 2017 Mar 28;146(12):124114. doi: 10.1063/1.4978958.
The well-established quantum cluster equilibrium (QCE) model provides a statistical thermodynamic framework to apply high-level ab initio calculations of finite cluster structures to macroscopic liquid phases using the partition function. So far, the harmonic approximation has been applied throughout the calculations. In this article, we apply an important correction in the evaluation of the one-particle partition function and account for anharmonicity. Therefore, we implemented an analytical approximation to the Morse partition function and the derivatives of its logarithm with respect to temperature, which are required for the evaluation of thermodynamic quantities. This anharmonic QCE approach has been applied to liquid hydrogen chloride and cluster distributions, and the molar volume, the volumetric thermal expansion coefficient, and the isobaric heat capacity have been calculated. An improved description for all properties is observed if anharmonic effects are considered.
成熟的量子团簇平衡（QCE）模型提供了一个统计热力学框架，可使用配分函数将有限团簇结构的高精度从头计算应用于宏观液相。到目前为止，整个计算过程都应用了简谐近似。在本文中，我们在评估单粒子配分函数时应用了一个重要的修正，并考虑了非谐性。因此，我们实现了 Morse 配分函数的解析逼近及其对数关于温度的导数，这是评估热力学量所必需的。这种非谐 QCE 方法已应用于液态氯化氢和团簇分布，并计算了摩尔体积、体积热膨胀系数和等压热容。如果考虑非谐效应，则所有性质的描述都会得到改善。
