Two Faces of the Two-Phase Thermodynamic Model,Journal of Chemical Theory and Computation

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Two Faces of the Two-Phase Thermodynamic Model
Journal of Chemical Theory and Computation ( IF 5.7 ) Pub Date : 2021-10-14 , DOI: 10.1021/acs.jctc.1c00156
Ádám Madarász ₁ , Andrea Hamza ₁ , Dávid Ferenc _{1,

2} , Imre Bakó ₁

Affiliation

The quantum harmonic model and the two-phase thermodynamic method (2PT) are widely used to obtain quantum-corrected properties such as isobaric heat capacities or molar entropies. 2PT heat capacities were calculated inconsistently in the literature. For water, the classical heat capacity was also considered, but for organic liquids, it was omitted. We reanalyzed the performance of different quantum corrections on the heat capacities of common organic solvents against experimental data. We have pointed out serious flaws in previous 2PT studies. The vibrational density of states was calculated incorrectly causing a 39% relative error in diffusion coefficients and 45% error in the 2PT heat capacities. The wrong conversion of isobaric and isochoric heat capacities also caused about 40% error but in the other direction. We have introduced the concept of anharmonic correction (AC), which is simply the deviation of the classical heat capacity from that of the harmonic oscillator model. This anharmonic contribution is around +30 to 40 J/(mol K) for water depending on the water model and −8 to −10 J/(mol K) for hydrocarbons and halocarbons. AC is unrealistically large, +40 J/(K mol) for alcohols and amines, indicating some deficiency of the OPLS force field. The accuracy of the computations was also assessed with the determination of the self-diffusion coefficients.

中文翻译：

两相热力学模型的两个面

量子调和模型和两相热力学方法 (2PT) 被广泛用于获得量子校正的属性，例如等压热容或摩尔熵。2PT 热容量在文献中计算不一致。对于水，还考虑了经典热容，但对于有机液体，则省略了。我们根据实验数据重新分析了不同量子校正对常见有机溶剂热容的性能。我们已经指出了之前 2PT 研究中的严重缺陷。状态的振动密度计算不正确，导致扩散系数的相对误差为 39%，2PT 热容的误差为 45%。等压和等容热容的错误转换也导致了大约 40% 的错误，但方向相反。我们已经引入了非谐波校正 (AC) 的概念，它只是经典热容与谐振子模型的偏差。根据水模型，这种非谐波贡献对于水约为 +30 至 40 J/(mol K)，而对于碳氢化合物和卤烃，则为 -8 至 -10 J/(mol K)。AC 大得不切实际，醇和胺为 +40 J/(K mol)，表明 OPLS 力场存在一些缺陷。计算的准确性也通过自扩散系数的确定来评估。AC 大得不切实际，醇和胺为 +40 J/(K mol)，表明 OPLS 力场存在一些缺陷。计算的准确性也通过自扩散系数的确定来评估。AC 大得不切实际，醇和胺为 +40 J/(K mol)，表明 OPLS 力场存在一些缺陷。计算的准确性也通过自扩散系数的确定来评估。

更新日期：2021-11-09

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