运动方程耦合簇方法计算三重态旋轨耦合分裂能以及单-三重态跃迁性质

磷光在发光材料，化学传感，生物成像等领域都有广泛应用，而磷光的辐射强度和寿命依赖于三重激发态旋轨耦合分裂能以及三重态和单重基态之间的跃迁矩。本项目计划从标量相对论EOM-CCSD方法出发，结合准简并微扰理论和一阶非简并微扰理论计算旋轨耦合效应，开发三重激发态分裂能和三重-单重态之间跃迁性质的计算方法和程序，用以研究闭壳层小分子体系的磷光辐射跃迁性质。我们所发展的方法与目前常用的相关计算方法相比，能解决三重激发态与其他激发态能量近简并的问题，适用于旋轨耦合效应较强的体系；由于考虑了所有电子态对微扰波函数的贡献，能给出较高精度的三重-单重态跃迁性质。此外，EOM-CCSD方法是单参考态方法，使用起来比多参考态方法更加简单，而且对单激发为主的激发态能给出较高精度的结果。本项目所得到的结果可以作为标准，为TDDFT研究大分子体系的磷光辐射跃迁时选择合适的交换相关泛函提供参考。

Phosphorescence has important applications in areas such as light-emitting materials, chemosensors and bioimaging. Phosphorescence intensity and lifetime depend on splittings of triplet state and triplet-singlet transition moments. In this project, we propose to develop computational methods and programs to calculate splittings of triplet state and triplet-singlet transition properties starting from scalar-relativistic EOM-CCSD calculations. A combination of quasidegenerate perturbation theory and first-order non-degenerate perturbation theory will be employed to deal with spin-orbit coupling (SOC) and the present approach will be applied to radiative phosphorescence emissions of small molecules. Compared with traditional methods, this approach is applicable to situations when other states are close to the target triplet state or when SOC is more pronounced. In addition, reasonable triplet-singlet transition properties can be achieved since contributions of all the states to the target states due to SOC is considered. EOM-CCSD is a single-reference approach and it is easier to be used than multireference approaches and reliable results can be obtained for transitions with a dominant single excitation character. Results achieved with the present method can be employed as reference to choose a proper exchange-correlation functional in TDDFT calculations for radiative phosphorescence emission processes of larger molecules.