Development of time-independent eigenstate-free methods for calculating vibronic spectra beyond the harmonic approximation

用量子化学方法计算分子的电子振动光谱，例如光电离光谱，受到高振动态密度的影响，并且一旦考虑到非谐效应，计算需求就会增加。最近，我们提供了一个原则的证明，最初开发的框架内的时间相关的方法，这是能够克服这些限制，避免显式计算的本征态的想法，也可以转移到时间无关的实现。这种基于非齐次薛定谔方程的与时间无关的拉曼波函数方法是全新的，尚未被详细研究。因此，需要探索如何以最有效和最稳健的方式求解相关方程的策略。除此之外，还应开发用于计算共振拉曼光谱的与时间无关的拉曼波函数理论，并对非谐波波函数进行实施。应进行依赖于从显式关联耦合簇或多参考方法获得的多维势能面的高精度计算，以便与实验数据进行直接比较。

The calculation of vibronic spectra, e.g. photoionization spectra, of molecules by quantum chemical approaches suffers from the high density of vibrational states and the computational demands once anharmonic effects shall be accounted for. Very recently, we provided a proof of principle that ideas originally developed within the framework of time-dependent methods, which are able to overcome these limitations and which avoid the explicit calculation of eigenstates, can also be transferred to time-independent implementations. Such a time-independent Raman wavefunction approach based on the inhomogeneous Schroedinger equation is completely new and has not yet been investigated in detail. As a consequence, strategies need to be explored, how to solve the associated equations in a most efficient and robust manner. Besides that, a time-independent Raman wavefunction theory for the calculation of resonance Raman spectra shall be developed and implemented for anharmonic wavefunctions. Highly accurate calculations relying on multi-dimensional potential energy surfaces obtained from explicitly correlated coupled-cluster or multireference methods shall be performed in order to allow for a direct comparison with experimental data.