Theophilou Iris, Tassi M, Thanos S
Peter Grunberg Institut (PGI) Forschungszentrum Jülich, D-52425 Jülich, Germany.
Institute for Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, 'Demokritos' National Center for Scientific Research, 15310 Athens, Greece.
J Chem Phys. 2014 Apr 28;140(16):164102. doi: 10.1063/1.4871502.
Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations.
光诱导电荷转移过程在新型光伏现象和器件中起着关键作用。因此，开发能够准确且计算成本低廉地处理电荷转移激发的从头算方法是当今吸引大量科学关注的一个课题。在本文中，我们扩展了一种最近引入的用于描述单重和双重激发的方法[M. 塔西、I. 西奥菲洛和S. 萨诺斯，《国际量子化学杂志》113, 690 (2013); M. 塔西、I. 西奥菲洛和S. 萨诺斯，《化学物理杂志》138, 124107 (2013)]，以允许描述分子间电荷转移激发。我们描述了一种激发过程，其中一个电子从供体系统转移到受体系统，使激发态与基态正交并避免变分坍缩。这些条件是通过将由哈特里 - 福克（HF）基态轨道所张成的空间分解为四个子空间来实现的：由定域在供体分子区域内的占据轨道所张成的子空间、受体分子对应的子空间以及另外两个分别包含定域在供体和受体附近的虚拟轨道的子空间。接下来，我们在供体的占据轨道子空间中创建一个有一个空穴且在受体的虚拟子空间中有一个粒子的斯莱特行列式。随后，我们通过在相应子空间中最小化HF能量泛函来优化空穴和粒子。最后，我们通过计算一组四氰基乙烯 - 烃配合物的最低电荷转移激发能来测试我们的方法，这些配合物此前已被用作此类激发的测试集。
