Institute of Material Science, Demokritos National Center for Scientific Research, 15310 Athens, Greece.
J Chem Phys. 2013 Mar 28;138(12):124107. doi: 10.1063/1.4797466.
Doubly excited states have nowadays become important in technological applications, e.g., in increasing the efficiency of solar cells and therefore, their description using ab initio methods is a great theoretical challenge as double excitations cannot be described by linear response theories based on a single Slater determinant. In the present work we extend our recently developed Hartree-Fock (HF) approximation for calculating singly excited states [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013)] in order to allow for the calculation of doubly excited states. We describe the double excitation as two holes in the subspace spanned from the occupied HF orbitals and two particles in the subspace of virtual HF orbitals. A subsequent minimization of the energy results to the determination of the spin orbitals of both the holes and the particles in the occupied and virtual subspaces, respectively. We test our method, for various atoms, H2 and polyene molecules which are known to have excitations presenting a significant double excitation character. Importantly, our approach is computationally inexpensive.
如今，双重激发态在技术应用中变得非常重要，例如，在提高太阳能电池的效率方面，因此，使用从头算方法来描述它们是一个巨大的理论挑战，因为双激发态不能用基于单个 Slater 行列式的线性响应理论来描述。在本工作中，我们扩展了我们最近开发的 Hartree-Fock（HF）方法来计算单重激发态[M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013)]，以便能够计算双重激发态。我们将双激发描述为占据 HF 轨道子空间中的两个空穴和虚拟 HF 轨道子空间中的两个粒子。随后，能量的最小化导致确定占据和虚拟子空间中空穴和粒子的自旋轨道。我们对各种原子、H2 和多烯分子进行了测试，这些分子已知具有表现出显著双重激发特征的激发态。重要的是，我们的方法计算成本低廉。
