Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, USA.
J Chem Phys. 2012 Jan 21;136(3):034306. doi: 10.1063/1.3674995.
The purpose of the present investigation is to calculate partition functions and thermodynamic quantities, viz., entropy, enthalpy, heat capacity, and Gibbs free energies, for 1-butanol, 2-methyl-1-propanol, and butanal in the vapor phase. We employed the multi-structural (MS) anharmonicity method and electronic structure calculations including both explicitly correlated coupled cluster theory and density functional theory. The calculations are performed using all structures for each molecule and employing both the local harmonic approximation (MS-LH) and the inclusion of torsional anharmonicity (MS-T). The results obtained from the MS-T calculations are in excellent agreement with experimental data taken from the Thermodynamics Research Center data series and the CRC Handbook of Chemistry and Physics, where available. They are also compared with Benson's empirical group additivity values, where available; in most cases, the present results are more accurate than the group additivity values. In other cases, where experimental data (but not group additivity values) are available, we also obtain good agreement with experiment. This validates the accuracy of the electronic structure calculations when combined with the MS-T method for estimating the thermodynamic properties of systems with multiple torsions, and it increases our confidence in the predictions made with this method for molecules and temperatures where experimental or empirical data are not available.
本研究的目的是计算 1-丁醇、2-甲基-1-丙醇和丁醛在气相中的配分函数和热力学量，即熵、焓、热容和吉布斯自由能。我们采用了多结构（MS）非谐性方法和电子结构计算，包括显式相关耦合簇理论和密度泛函理论。计算是针对每个分子的所有结构进行的，并采用局部谐波近似（MS-LH）和包括扭转非谐性（MS-T）。MS-T 计算得到的结果与来自热力学研究中心数据系列和 CRC 手册的实验数据非常吻合，在可用的情况下。它们还与本森的经验基团加和值进行了比较，在大多数情况下，本研究的结果比基团加和值更准确。在其他情况下，虽然有实验数据（但没有基团加和值），我们也与实验结果吻合得很好。这验证了在估计具有多个扭转的系统的热力学性质时，将电子结构计算与 MS-T 方法结合使用的准确性，并增加了我们对该方法在分子和温度下进行预测的信心，在这些情况下，没有实验或经验数据。
