多态CASPT2理论的解析导数耦合
Analytical derivative coupling for multistate CASPT2 theory
摘要：
光化学动力学中非辐射跃迁的概率由导数耦合决定，即不同电子态之间通过核自由度的耦合。因此，有效和准确地评价衍生物的耦合是至关重要的，以实现可靠的计算机模拟的光化学反应。本文研究了多态多参考二阶微扰理论（MS-CASPT 2）及其“扩展”变体（XMS-CASPT 2）的导数耦合，并给出了一个解析计算算法。计算导数耦合的计算成本基本上与计算核能梯度的计算成本相同。用XMS-CASPT 2计算的小分子在最小能量圆锥交叉点（MECIs）的几何构型和能量与多参考组态相互作用计算的结果吻合较好。作为数值示例，使用XMS-CASPT 2针对芪和GFP模型发色团（4-对羟基亚苄基-1，2-二甲基-咪唑啉-5-酮阴离子）优化MECI。
英文摘要：
The probability of non-radiative transitions in photochemical dynamics is determined by the derivative couplings, the couplings between different electronic states through the nuclear degrees of freedom. Efficient and accurate evaluation of the derivative couplings is, therefore, of central importance to realize reliable computer simulations of photochemical reactions. In this work, the derivative couplings for multistate multireference second-order perturbation theory (MS-CASPT2) and its 'extended' variant (XMS-CASPT2) are studied, in which we present an algorithm for their analytical evaluation. The computational costs for evaluating the derivative couplings are essentially the same as those for calculating the nuclear energy gradients. The geometries and energies calculated with XMS-CASPT2 for small molecules at minimum energy conical intersections (MECIs) are in good agreement with those computed by multireference configuration interaction. As numerical examples, MECIs are optimized using XMS-CASPT2 for stilbene and a GFP model chromophore (the 4-para-hydroxybenzylidene-1,2-dimethyl-imidazolin-5-one anion).
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