Large-scale calculations of gas phase thermochemistry: Enthalpy of formation, standard entropy, and heat capacity
Large-scale calculations of gas phase thermochemistry: Enthalpy of formation, standard entropy, and heat capacity
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DOI：
10.1063/1.4962627
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发表时间：
2016-09-21
影响因子：
4.4
通讯作者：
van der Spoel, David
中科院分区：
文献类型：
--
作者：
Ghahremanpour, Mohammad M.;van Maaren, Paul J.;van der Spoel, David
给出了摩尔生成焓（Delta（f）H-0）、标准熵（S-0）和热容（C-V）的大尺度量子计算。一个大的数据集可能有助于评估量子热化学工具，以发现可能隐藏的缺点，并找到可能需要重新研究的实验数据，事实上，我们列出并注释了大约200个有问题的热化学测量。如果只考虑单一（最小能量）构象，量子方法系统地低估了气相中柔性分子的S-0。这个问题原则上可以通过对所有稳定构象进行热化学计算来解决[Zheng等人，Phys.Chem.Chem.Phys.13，10885-10907（2011）]，但这对于大分子是不实际的。我们观察到复合量子热化学配方与实验S-0的偏差大致对应于玻尔兹曼方程（S = R ln Ω），其中R是气体常数，Ω是可能构象的数量。这允许对具有多种构象的分子的计算熵进行经验校正。对1273个化合物的实验数据进行了修正，得到了近似为13 J/mol K的RMSD。本文还提供了超过700种化合物的Delta（f）H-0，S-0和C-V的预测，这些化合物在文献中没有实验数据。最后，为了便于其他人分析热力学性质，我们在OpenBabel程序套件中实现了一个新的工具obthermo [O 'Boyle等人，J. Cheminf. 3，33（2011）]，包括用于流行的热化学方法的参考原子化能量值的表。(C)2016年作者。所有文章内容，除非另有说明，是根据知识共享署名（CC BY）许可证（http：//creativecommons.org/licenses/by/4.0/）。
Large scale quantum calculations for molar enthalpy of formation (Delta(f) H-0), standard entropy (S-0), and heat capacity (C-V) are presented. A large data set may help to evaluate quantum thermochemistry tools in order to uncover possible hidden shortcomings and also to find experimental data that might need to be reinvestigated, indeed we list and annotate approximately 200 problematic thermochemistry measurements. Quantum methods systematically underestimate S-0 for flexible molecules in the gas phase if only a single (minimum energy) conformation is taken into account. This problem can be tackled in principle by performing thermochemistry calculations for all stable conformations [Zheng et al., Phys. Chem. Chem. Phys. 13, 10885-10907 (2011)], but this is not practical for large molecules. We observe that the deviation of composite quantum thermochemistry recipes from experimental S-0 corresponds roughly to the Boltzmann equation (S = R ln Omega), where R is the gas constant and Omega the number of possible conformations. This allows an empirical correction of the calculated entropy for molecules with multiple conformations. With the correction we find an RMSD from experiment of approximate to 13 J/mol K for 1273 compounds. This paper also provides predictions of Delta(f) H-0, S-0, and C-V for well over 700 compounds for which no experimental data could be found in the literature. Finally, in order to facilitate the analysis of thermodynamics properties by others we have implemented a new tool obthermo in the OpenBabel program suite [O'Boyle et al., J. Cheminf. 3, 33 (2011)] including a table of reference atomization energy values for popular thermochemistry methods. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).