Chemically Accurate Vibrational Free Energies of Adsorption from Density Functional Theory Molecular Dynamics: Alkanes in Zeolites.
Chemically Accurate Vibrational Free Energies of Adsorption from Density Functional Theory Molecular Dynamics: Alkanes in Zeolites.
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DOI：
10.1021/acs.jctc.1c00519
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发表时间：
2021-09-14
影响因子：
5.5
通讯作者：
Sauer J
中科院分区：
文献类型：
--
作者：
Galimberti DR;Sauer J
我们提出了一种方法来计算，在减少计算成本，吉布斯自由能，焓和熵的吸附从分子动力学。我们从振动能量中计算振动配分函数，振动能量是由态的振动密度通过在法模上的投影得到的。沿着轨迹使用一组精心选择的参考结构可以解释模态的非调和性。对于H-CHA沸石对甲烷、乙烷和丙烷的吸附，我们将处理限制在吸附位点（沸石羟基）和与之相互作用的烷烃分子上的一组振动模式。只需要两个短轨迹（1 - 20 ps）就可以达到热力学函数的收敛（<1 kJ/mol）。Gibbs自由能、焓和熵项（−TΔS）与实验测量值的平均绝对偏差分别为2.6、2.8和4.7 kJ/mol。特别是，与谐波近似相比，熵项有了很大的改进，几乎达到了以前使用单个模态的曲线畸变获得的非谐波频率的精度。得到的热力学函数与甲烷、乙烷和丙烷的实验值的变化趋势一致，并正确地预测了实验条件下吸附的吉布斯自由能由甲烷的正（5.9 kJ/mol）变为乙烷的负（- 4.8 kJ/mol）和丙烷的负（- 7.1 kJ/mol）。
We present a methodology to compute, at reduced computational cost, Gibbs free energies, enthalpies, and entropies of adsorption from molecular dynamics. We calculate vibrational partition functions from vibrational energies, which we obtain from the vibrational density of states by projection on the normal modes. The use of a set of well-chosen reference structures along the trajectories accounts for the anharmonicities of the modes. For the adsorption of methane, ethane, and propane in the H-CHA zeolite, we limit our treatment to a set of vibrational modes localized at the adsorption site (zeolitic OH group) and the alkane molecule interacting with it. Only two short trajectories (1–20 ps) are required to reach convergence (<1 kJ/mol) for the thermodynamic functions. The mean absolute deviations from the experimentally measured values are 2.6, 2.8, and 4.7 kJ/mol for the Gibbs free energy, the enthalpy, and the entropy term (−TΔS), respectively. In particular, the entropy terms show a major improvement compared to the harmonic approximation and almost reach the accuracy of the previous use of anharmonic frequencies obtained with curvilinear distortions of individual modes. The thermodynamic functions so obtained follow the trend of the experimental values for methane, ethane, and propane, and the Gibbs free energy of adsorption at experimental conditions is correctly predicted to change from positive for methane (5.9 kJ/mol) to negative for ethane (−4.8 kJ/mol) and propane (−7.1 kJ/mol).
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