In this work, we present an altered partition function that leads to an improved calculation of the enthalpy and entropy of vaporization in the framework of quantum cluster equilibrium theory. The changes are based on a previously suggested modification [S. Grimme, Chem. Eur. J. 18, 9955–9964 (2012)] of the molecular entropy calculation in the gas phase. Here, the low energy vibrational frequencies in the vibrational partition function are treated as hindered rotations instead of vibrations. The new scheme is tested on a set of nine organic solvents for the calculation of the enthalpy and entropy of vaporization. The enthalpies and entropies of vaporization show improvements from 6.5 error to 3.3 kJ mol⁻¹ deviation to experiment and from 28.4 error to 13.5 J mol⁻¹ K⁻¹ deviation to experiment, respectively. The effect of the corrected partition function is visible in the different populations of clusters, which become physically more meaningful in that larger clusters are higher populated in the liquid phase and the gas phase is mainly populated by the monomers. Furthermore, the corrected partition function also overcomes technical difficulties and leads to an increased stability of the calculations in regard to the size of the cluster set.

中文翻译：

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量子簇平衡理论中改进的分配函数计算改进的汽化焓和熵

在这项工作中，我们提出了一个改变的分配函数，它可以在量子簇平衡理论的框架内改进汽化焓和熵的计算。这些更改基于先前建议的修改 [S. 格林，化学。欧元。J. 18 , 9955–9964 (2012)] 气相中的分子熵计算。这里，振动分配函数中的低能量振动频率被视为受阻旋转而不是振动。新方案在一组九种有机溶剂上进行了测试，以计算蒸发的焓和熵。蒸发的焓和熵显示从 6.5 误差改善到 3.3 kJ mol ^-1实验偏差，从 28.4 误差改善到 13.5 J mol ^-1分别与实验的 K ^-1偏差。校正分配函数的效果在不同的簇群中是可见的，这在物理上变得更有意义，因为较大的簇在液相中的填充量更高，而气相主要由单体填充。此外，校正后的分区函数还克服了技术难题，并提高了关于簇集大小的计算稳定性。