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首页> 外文期刊>Journal of chemical theory and computation: JCTC >A Practical Computational Approach to Study Molecular Instability Using the Pseudo-Jahn-Teller Effect
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A Practical Computational Approach to Study Molecular Instability Using the Pseudo-Jahn-Teller Effect

机译：利用伪Jahn-Teller效应研究分子不稳定性的实用计算方法

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摘要

Vibronic coupling theory shows that the cause for spontaneous instability in systems presenting a nondegenerate ground state is the so-called pseudo-Jahn—Teller effect, and thus its study can be extremely, helpfol to understand the structure of many molecules. While this theory, based on the mixing of the ground and excited states with a distortion, has been long studied, there are two obscure points that we try to clarify in the present work. First, the operators involved in both the vibronic and nonvibronic parts of the force constant talte only into account electron—nuclear and nuclear—nuclear interactions, apparently leaving electron—electron repulsions and the electron's kinetic energy out of the chemical picture. Second, a fully quantitative, computational appraisal of this effect has been up to now problematic. Here, we present a reformulation of the pseudo-Jahn- Teller theory that explicitly shows the contributions of all operators in the molecular Hamiltonian and allows connecting the results obtained with this model to other chemical theories relating electron distribution and geometry. Moreover, we develop a practical approach based on Hartree—Fock and density functional theory that allows quantification of the pseudo-Jahn—Teller effect We demonstrate the usefulness of our method studying the pyramidal distortion in ammonia and its absence in borane, revealing the strong importance of the kinetic energy of the electrons in the lowest a2n orbital to trigger this instability. The present tool opens a window for exploring in detail the actual microscopic origin of structural instabilities in molecules and solids.
机译：振动耦合理论表明，在呈现简并基态的系统中，自发不稳定的原因是所谓的拟Jahn-Teller效应，因此其研究可以极大地帮助理解许多分子的结构。虽然已经对基于基态和激发态与畸变的混合的理论进行了长期的研究，但在本文中我们试图澄清两个模糊的点。首先，涉及力常数的振动和非振动部分的算子仅考虑到电子-核和核-核相互作用，显然使电子-电子排斥和电子的动能不在化学范围之内。第二，到目前为止，对该效果进行完全定量的计算评估一直是有问题的。在这里，我们提出一种拟Jahn-Teller理论的重新表述，该理论明确显示了分子哈密顿量中所有算子的贡献，并将该模型获得的结果与涉及电子分布和几何学的其他化学理论相联系。此外，我们基于Hartree-Fock和密度泛函理论开发了一种实用的方法，可以对拟Jahn-Teller效应进行量化。我们证明了研究氨中的金字塔形畸变以及在硼烷中不存在金字塔形畸变的方法的有用性，从而显示出强烈的重要性在最低的a2n轨道中，电子的动能会触发这种不稳定性。本工具打开一个窗口，用于详细探讨分子和固体中结构不稳定性的实际微观起源。

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