Investigation and modelling of dispersion interactions in electronically excited states and the effects of dispersion interactions on electronic excitations

该项目的目的是更好地了解发色团中的电子激发及其与环境的弥散相互作用之间的联系。要解决的重要研究问题是：在哪些化学情况下，对于哪种电子激发态，在其量子化学描述中考虑色散相互作用在电子激发时的变化是重要的？是否存在色散与环境的相互作用显著改变激发态的激发能或电子结构或激发态的有序性的情况和/或生色团？本项目的另一个目标是发展色散对自洽反应场模型PE(极化嵌入)的贡献，该模型在计算基态和电子激发态的波函数参数时考虑色散相互作用。因此，将避免后验修正，因为它们通常在避免的交叉附近导致定性错误的势能面。这是因为我们针对的是一种QM/MM方法，它包含了电子激发过程中的色散相互作用，适合于计算激发态结构和驰豫过程。这将在Peri-ADC(2)和Peri-CC2方法的例子中实现。对于用相关波函数方法计算较大分子的色散系数，我们还将扩展现有的RI-CC2代码，用于虚频率的基态和激发态随频率变化的极化率以及柯西矩的计算。

The aim of the project is to achieve a better understanding of the connection between the electronic excitations in a chromophore and its dispersion interaction with an environment. Important research questions that will be addressed are: In which chemical situations and for which kind of electronically excited states is it important to account for the change of the dispersion interaction upon electronic excitation in its quantum chemical description? Are there situations and/or chromophores where the dispersion interaction with the environment changes significantly the excitation energy or the electronic structure of the excited state or the order of the excited states?An additional object of the project is the development of the dispersion contribution to the self-consistent reaction field model PE (polarizable embedding) which accounts for the dispersion interaction during the calculation of the wavefunction parameters for the ground and electronically excited states. A posteriori corrections will thereby be avoided because they lead in general to qualitatively wrong potential energy surfaces in the vicinity of avoided crossings. This is done because we aim at a QM/MM method, which includes the dispersion interaction upon electronic excitation processes and is suitable for the calculation of excited state structures and relaxation processes. This will be implemented at the example of the PERI-ADC(2) and PERI-CC2 methods.For the computation of dispersion coefficients for larger molecules with a correlated wavefunction method we will in addition extend an existing RI-CC2 code for frequency-dependent polarizabilities in ground and excited states for imaginary frequency and for the calculation of Cauchy moments.