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The multi-configuration time-dependent Hartree (MCTDH) method was applied to study nuclear dynamics following transitions to a manifold of vibronically coupled ground 2A1 and excited 2A2 and 2B1 states of the pyridine radical cation (PRC). These states originate from ionization out of the highest occupied orbitals of pyridine, 7a1 (nσ), 1a2 (π), and 2b1 (π), respectively, and give rise to the lowest two photoelectron bands. We focus on various theoretical and computational aspects of the MCTDH method and methodology to calculate the spectrum, taking our study of the vibronically interacting 2A1, 2A2, and 2B1 states of PRC as an example. In particular, the choice of the single-particle functions (SPFs) and schemes to combine vibrational modes are discussed.

An earlier developed electron propagator method for the treatment of electron attachment to molecules within the non-Dyson algebraic-diagrammatic construction framework (EA-ADC) is extended by inclusion of the complex absorbing potential (CAP). The resulting method allows for the investigation of resonance states of metastable anions. Approximation schemes up to third-order perturbation theory for the electron propagator (EA-ADC(3)) are implemented. The CAP operator is treated up to second-order using the intermediate state representation formalism (ISR(2)) and the subspace projection technique. The CAP/EA-ADC(3) method is tested in first applications to the resonances in CO and N2 molecules associated with electron attachment to their low-lying π*-orbitals. The results of the calculations agree well with the available experimental and theoretical data and demonstrate the CAP-augmented EA-ADC modeling can become a useful tool for theoretical studies of metastable electron-attached states.