Lyskov Igor, Kleinschmidt Martin, Marian Christel M
Institute of Theoretical and Computational Chemistry, Heinrich-Heine-University Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany.
J Chem Phys. 2016 Jan 21;144(3):034104. doi: 10.1063/1.4940036.
The combined density functional theory and multireference configuration interaction (DFT/MRCI) method of Grimme and Waletzke [J. Chem. Phys. 111, 5645 (1999)] is a well-established semi-empirical quantum chemical method for efficiently computing excited-state properties of organic molecules. As it turns out, the method fails to treat bi-chromophores owing to the strong dependence of the parameters on the excitation class. In this work, we present an alternative form of correcting the matrix elements of a MRCI Hamiltonian which is built from a Kohn-Sham set of orbitals. It is based on the idea of constructing individual energy shifts for each of the state functions of a configuration. The new parameterization is spin-invariant and incorporates less empirism compared to the original formulation. By utilizing damping techniques together with an algorithm of selecting important configurations for treating static electron correlation, the high computational efficiency has been preserved. The robustness of the original and redesigned Hamiltonians has been tested on experimentally known vertical excitation energies of organic molecules yielding similar statistics for the two parameterizations. Besides that, our new formulation is free from artificially low-lying doubly excited states, producing qualitatively correct and consistent results for excimers. The way of modifying matrix elements of the MRCI Hamiltonian presented here shall be considered as default choice when investigating photophysical processes of bi-chromophoric systems such as singlet fission or triplet-triplet upconversion.
格林姆和瓦莱茨克提出的组合密度泛函理论与多参考组态相互作用（DFT/MRCI）方法[《化学物理杂志》111, 5645 (1999)]是一种成熟的半经验量子化学方法，用于高效计算有机分子的激发态性质。事实证明，由于参数对激发类别的强烈依赖性，该方法无法处理双色团。在这项工作中，我们提出了一种修正由一组科恩-沈轨道构建的MRCI哈密顿量矩阵元的替代形式。它基于为组态的每个态函数构建单独能量位移的思想。新的参数化是自旋不变的，与原始公式相比包含的经验性更少。通过使用阻尼技术以及一种选择重要组态来处理静态电子关联的算法，保持了高计算效率。在有机分子的实验已知垂直激发能上测试了原始和重新设计的哈密顿量的稳健性，两种参数化得到了相似的统计结果。除此之外，我们的新公式没有人为的低能双激发态，对激基缔合物产生了定性正确且一致的结果。当研究双色团体系的光物理过程，如单线态裂变或三线态-三线态上转换时，这里提出的修改MRCI哈密顿量矩阵元的方法应被视为默认选择。
