Theoretische Chemie, Universität Bielefeld, Postfach 100131, D-33501 Bielefeld, Germany.
J Chem Phys. 2012 Aug 14;137(6):064101. doi: 10.1063/1.4740248.
A new method has been reported recently [H. Ndome, R. Welsch, and W. Eisfeld, J. Chem. Phys. 136, 034103 (2012)] that allows the efficient generation of fully coupled potential energy surfaces (PESs) including derivative and spin-orbit (SO) coupling. The method is based on the diabatic asymptotic representation of the molecular fine structure states and an effective relativistic coupling operator and therefore is called effective relativistic coupling by asymptotic representation (ERCAR). The resulting diabatic spin-orbit coupling matrix is constant and the geometry dependence of the coupling between the eigenstates is accounted for by the diabatization. This approach allows to generate an analytical model for the fully coupled PESs without performing any ab initio SO calculations (except perhaps for the atoms) and thus is very efficient. In the present work, we study the performance of this new method for the example of hydrogen iodide as a well-established test case. Details of the diabatization and the accuracy of the results are investigated in comparison to reference ab initio calculations. The energies of the adiabatic fine structure states are reproduced in excellent agreement with reference ab initio data. It is shown that the accuracy of the ERCAR approach mainly depends on the quality of the underlying ab initio data. This is also the case for dissociation and vibrational level energies, which are influenced by the SO coupling. A method is presented how one-electron operators and the corresponding properties can be evaluated in the framework of the ERCAR approach. This allows the computation of dipole and transition moments of the fine structure states in good agreement with ab initio data. The new method is shown to be very promising for the construction of fully coupled PESs for more complex polyatomic systems to be used in quantum dynamics studies.
最近报道了一种新方法[H. Ndome、R. Welsch 和 W. Eisfeld，J. Chem. Phys. 136, 034103 (2012)]，可高效生成包含导数和自旋轨道（SO）耦合的完全耦合势能面（PES）。该方法基于分子精细结构态的绝热渐近表示和有效的相对论耦合算符，因此称为有效相对论耦合的渐近表示（ERCAR）。所得的绝热 SO 耦合矩阵是常数，本征态之间的耦合的几何依赖性通过绝热化来考虑。该方法允许生成完全耦合 PES 的解析模型，而无需执行任何从头算 SO 计算（除了原子），因此非常高效。在本工作中，我们以碘化氢为例研究了这种新方法的性能，碘化氢是一个经过充分验证的测试案例。与参考从头算计算相比，研究了绝热化和结果准确性的细节。通过与参考从头算数据的极好一致性，再现了绝热精细结构态的能量。结果表明，ERCAR 方法的准确性主要取决于基础从头算数据的质量。这对于解离和振动能级也是如此，SO 耦合会影响它们。提出了一种方法，用于在 ERCAR 方法框架中评估单电子算符和相应的性质。这允许与从头算数据很好地一致地计算精细结构态的偶极矩和跃迁矩。新方法在构建用于量子动力学研究的更复杂多原子体系的完全耦合 PES 方面显示出很有前途。
