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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >A Diabatic Representation Including Both Valence Nonadiabatic Interactions and Spin-Orbit Effects for Reaction Dynamics
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A Diabatic Representation Including Both Valence Nonadiabatic Interactions and Spin-Orbit Effects for Reaction Dynamics

机译：包含价非绝热相互作用和反应动力学自旋轨道效应的绝热表示

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摘要

A diabatic representation is convenient in the study of electronically nonadiabatic chemical reactions because the diabatic energies and couplings are smooth functions of the nuclear coordinates and the couplings are scalar quantities. A method called the fourfold way was devised in our group to generate diabatic representations for spin-free electronic states. One drawback of diabatic states computed from the spin-free Hamiltonian, called a valence diabatic representation, for systems in which spin-orbit coupling cannot be ignored is that the couplings between the states are not zero in asymptotic regions, leading to difficulties in the calculation of reaction probabilities and other properties by semiclassical dynamics methods. Here we report an extension of the fourfold way to construct diabatic representations suitable for spin-coupled systems. In this article we formulate the method for the case of even-electron systems that yield pairs of fragments with doublet spin multiplicity. For this type of system, we introduce the further simplification of calculating the triplet diabatic energies in terms of the singlet diabatic energies via Slater's rules and assuming constant ratios of Coulomb to exchange integrals. Furthermore, the valence diabatic couplings in the triplet manifold are taken equal to the singlet ones. An important feature of the method is the introduction of scaling functions, as they allow one to deal with multibond reactions without having to include high-energy diabatic states. The global transformation matrix to the new diabatic representation, called the spin-valence diabatic representation, is constructed as the product of channel-specific transformation matrices, each one taken as the product of an asymptotic transformation matrix and a scaling function that depends on ratios of the spin-orbit splitting and the valence splittings. Thus the underlying basis functions are recoupled into suitable diabatic basis functions in a manner that provides a multibond generalization of the switch between Hund's cases in diatomic spectroscopy. The spin-orbit matrix elements in this representation are taken equal to their atomic values times a scaling function that depends on the internuclear distances. The spin-valence diabatic potential energy matrix is suitable for semiclassical dynamics simulations. Diagonalization of this matrix produces the spin-coupled adiabatic energies. For the sake of illustration, diabatic potential energy matrices are constructed along bond-fission coordinates for the HBr and the BrCH_2Cl molecules. Comparison of the spin-coupled adiabatic energies obtained from the spin-valence diabatics with those obtained by ab initio calculations with geometry-dependent spin-orbit matrix elements shows that the new method is sufficiently accurate for practical purposes. The method formulated here should be most useful for systems with a large number of atoms, especially heavy atoms, and/or a large number of spin-coupled electronic states.
机译：非绝热表示法在电子非绝热化学反应的研究中很方便，因为绝热能量和耦合是核坐标的平滑函数，而耦合是标量。我们小组设计了一种称为四重方式的方法来生成无旋转电子状态的非绝热表示。对于不能忽略自旋轨道耦合的系统，从无自旋哈密顿量计算的非绝热状态的一个缺点是价态非绝热表示，这是因为在渐近区域中状态之间的耦合不为零，从而导致计算困难半经典动力学方法确定反应概率和其他性质。在这里，我们报告了四重方式的扩展，以构造适合自旋耦合系统的非绝热表示形式。在本文中，我们针对偶数电子系统的情况制定了方法，该系统产生具有双重态自旋多重性的片段对。对于这种类型的系统，我们引入了进一步的简化方法，即通过Slater规则，根据单重非绝热能量来计算三重态非绝热能量，并假定库仑比率恒定，以交换积分。此外，三重态歧管中的​​价非绝热偶合等于单重态。该方法的一个重要特点是引入了缩放函数，因为它们允许人们处理多键反应而不必包括高能非绝热态。新的非绝热表示形式的整体变换矩阵称为自旋价非绝热表示形式，其构造是特定于通道的变换矩阵的乘积，每个矩阵都作为渐近变换矩阵和比例函数的乘积，比例函数取决于自旋轨道分裂和价分裂。因此，以提供双原子光谱中的洪德案例之间的转换的多键泛化的方式，将基础基础函数重新耦合为合适的非绝热基础函数。该表示中的自旋轨道矩阵元素等于其原子值乘以取决于核间距的缩放函数。自旋价绝热势能矩阵适用于半经典动力学模拟。该矩阵的对角线化产生自旋耦合的绝热能量。为便于说明，沿着HBr和BrCH_2Cl分子的键裂变坐标构建了非绝热势能矩阵。从自旋价绝热体获得的自旋耦合绝热能量与通过与几何相关的自旋轨道矩阵元素从头算得到的自耦耦合绝热能量的比较表明，该新方法对于实际目的是足够准确的。在此提出的方法对于具有大量原子，尤其是重原子和/或大量自旋耦合电子态的系统最有用。

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