Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, United States.
Dipartimento di Chimica, Università Degli Studi di Milano, via Golgi 19, 20133 Milano, Italy.
J Chem Theory Comput. 2022 Sep 13;18(9):5527-5538. doi: 10.1021/acs.jctc.2c00760. Epub 2022 Aug 11.
Ethanol is a molecule of fundamental interest in combustion, astrochemistry, and condensed phase as a solvent. It is characterized by two methyl rotors and () and conformers, which are known to be very close in energy. Here we show that based on rigorous quantum calculations of the vibrational zero-point state, using a new potential energy surface (PES), the ground state resembles the conformer, but substantial delocalization to the conformer is present. This explains experimental issues about identification and isolation of the two conformers. This "leak" effect is partially quenched when deuterating the OH group, which further demonstrates the need for a quantum mechanical approach. Diffusion Monte Carlo and full-dimensional semiclassical dynamics calculations are employed. The new PES is obtained by means of a Δ-machine learning approach starting from a pre-existing low level density functional theory surface. This surface is brought to the CCSD(T) level of theory using a relatively small number of CCSD(T) energies. Agreement between the corrected PES and direct results for standard tests is excellent. One- and two-dimensional discrete variable representation calculations focusing on the - torsional motion are also reported, in reasonable agreement with experiment.
乙醇作为燃烧、天体化学和凝聚相溶剂中的一个基本分子，具有两个甲基转子和 ()和 构象，它们的能量非常接近。在这里，我们表明，基于对振动零点能的严格量子计算，使用新的 势能面（PES），基态类似于 构象，但存在大量的向 构象的离域。这解释了关于两种构象的鉴定和分离的实验问题。当氘代 OH 基团时，这种“泄漏”效应会部分被抑制，这进一步证明了需要进行量子力学方法的研究。扩散蒙特卡罗和全维半经典动力学计算被采用。新的 PES 通过从现有的低水平密度泛函理论表面开始的 Δ-机器学习方法获得。使用相对较少的 CCSD(T) 能量，将该表面提升到 CCSD(T) 理论水平。修正后的 PES 与直接 结果之间的标准测试吻合得非常好。还报告了聚焦于 -扭转运动的一维和二维离散变量表示计算，与实验结果相当吻合。
