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

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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.