Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
J Chem Phys. 2011 Aug 28;135(8):081106. doi: 10.1063/1.3633329.
The extended multireference quasi-degenerate perturbation theory, proposed by Granovsky [J. Chem. Phys. 134, 214113 (2011)], is combined with internally contracted multi-state complete active space second-order perturbation theory (XMS-CASPT2). The first-order wavefunction is expanded in terms of the union of internally contracted basis functions generated from all the reference functions, which guarantees invariance of the theory with respect to unitary rotations of the reference functions. The method yields improved potentials in the vicinity of avoided crossings and conical intersections. The theory for computing nuclear energy gradients for MS-CASPT2 and XMS-CASPT2 is also presented and the first implementation of these gradient methods is reported. A number of illustrative applications of the new methods are presented.
由 Granovsky [J. Chem. Phys. 134, 214113 (2011)] 提出的扩展多参考准简并微扰理论与内收缩多态完全活性空间二级微扰理论 (XMS-CASPT2) 相结合。一阶波函数展开为所有参考函数生成的内收缩基函数的并集，这保证了理论对参考函数的幺正旋转的不变性。该方法在避免交叉点和圆锥交叉点附近产生改进的势能。还提出了用于 MS-CASPT2 和 XMS-CASPT2 计算核能梯度的理论，并报告了这些梯度方法的首次实现。展示了新方法的一些说明性应用。
