Identification of Torsional Modes in Complex Molecules Using Redundant Internal Coordinates: The Multistructural Method with Torsional Anharmonicity with a Coupled Torsional Potential and Delocalized Torsions,Journal of Chemical Theory and Computation

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Identification of Torsional Modes in Complex Molecules Using Redundant Internal Coordinates: The Multistructural Method with Torsional Anharmonicity with a Coupled Torsional Potential and Delocalized Torsions
Journal of Chemical Theory and Computation ( IF 5.7 ) Pub Date : 2022-11-28 , DOI: 10.1021/acs.jctc.2c00952
Wenqi Chen ₁ , Pengchao Zhang ₁ , Donald G Truhlar ₂ , Jingjing Zheng ₃ , Xuefei Xu ₁

Affiliation

Identification of internal-rotation modes in the normal-mode analysis of complex molecules is important for accurately describing the thermodynamic properties and kinetics of complex molecules when it is necessary to treat the anharmonicity of torsions and the multiconformer anharmonicity caused by the internal rotations. However, identifying and distinguishing torsional modes are very challenging because they are coupled to one another. In this work, we present a new strategy to automatically identify torsional vibrations and separate them from the other vibrational modes. By combining a redundant-internal-coordinate auto-generation procedure with torsional projection techniques, we automate the procedure of identifying and separating the coupled torsions, and we show that we can obtain robust and consistent results with various reasonable definitions of redundant-internal-coordinate sets. This model has been implemented in a new development version of the MSTor program to reduce the user input needed for multistructural and torsional anharmonicity (MS-T) calculations. The new method is called multistructural and torsional anharmonicity with a coupled torsional potential and delocalized torsions ([MS-T(CD)]. As example applications, we consider MS-T(CD) calculations on three molecules (2-hexyl radical, n-propylbenzene, and 5-hydroperoxy-6-oxohexanoylperoxy radical) that have multiple rotors and that provide challenges to choosing good sets of nonredundant-internal coordinates, and we compare the performance of the new strategy to five other torsion identification methods. The new strategy is demonstrated to be efficient in separating the torsional and nontorsional elements in the Hessian matrix, as well as in providing reasonable projected nontorsional frequencies to be used for calculations of partition function and thermochemistry.

中文翻译：

使用冗余内坐标识别复杂分子中的扭转模式：具有扭转非调和耦合扭转势和离域扭转的多结构方法

在复杂分子的正模分析中识别内旋模式对于准确描述复杂分子的热力学性质和动力学非常重要，因为需要处理扭转的非谐性和由内旋引起的多构象非谐性。然而，识别和区分扭转模式非常具有挑战性，因为它们相互耦合。在这项工作中，我们提出了一种自动识别扭转振动并将其与其他振动模式分开的新策略。通过将冗余内坐标自动生成程序与扭转投影技术相结合，我们可以自动执行识别和分离耦合扭转的过程，并且我们表明我们可以通过各种合理的冗余内部坐标集定义获得稳健且一致的结果。该模型已在新的开发版本中实现MSTor程序可减少多结构和扭转非谐性 (MS-T) 计算所需的用户输入。这种新方法称为多结构和扭转非谐性，具有耦合扭转势和离域扭转 ([MS-T(CD)]。作为示例应用，我们考虑对三个分子（2-己基自由基，n-丙苯和 5-hydroperoxy-6-oxohexanoylperoxy 自由基）具有多个转子，这对选择好的非冗余内坐标集提出了挑战，我们将新策略的性能与其他五种扭转识别方法进行了比较。新策略被证明可有效分离 Hessian 矩阵中的扭转和非扭转元素，以及提供合理的预计非扭转频率以用于配分函数和热化学的计算。

更新日期：2022-11-28

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