First principles calculations of molecules and materials will be conducted on advanced solar energy conversion processes, including dye-sensitized solar cells, artificial photosynthesis, and organic solar cells. The complexity of these systems, both in terms in molecular structure (supramolecular and nanostructured materials) and function (photoinduced processes involving excited states), makes it vital to use high-performance computing facilities for accurate computational studies. The ambition here is firstly to provide a better understanding of how solar energy conversion systems function on the molecular level, and secondly to use accurate calculations with predictive capability to guide the search for more efficient molecular components in such systems. We mainly use Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) calculations, complemented with reactive molecular dynamics simulations as well as high level ab initio methods. A. Excited State Evolution of Light-harvesting molecules A1. Excited states of molecular systems will be studied quantum chemically using first principles (time-dependent DFT and multi-reference ab initio) methods. Focus areas include excitation energies and potential energy surfaces (PESs) of dye molecules to predict the structure of excited state deactivation pathways and charge-separation. Ab initio molecular dynamics (AIMD) will be added to generate both structural and electronic reorganizations. B. Molecularly Functionalized Nanocrystals The structure and stability of metal oxide nanocrystals, e.g. TiO2, will be investigated using a combination of quantum chemical structure optimizations and molecular dynamics simulations on realistic atomistic models in the 1 - 10 nm size range. Electronic properties, will be calculated e.g. at the DFT and TD-DFT levels of theory for oxide and III-V semiconducting nanocrystalline materials. This requires use of larger cluster models, say (TiO2)n with n>100. C. Heterogeneous interfaces and catalysis A multi-scale combination of state-of-the-art quantum chemical calculations and molecular dynamics simulations (including in-house reaction-diffusion molecular dynamics simulation methods currently under development) will be applied to studies of molecular functionalization of metal oxide substrates and heterogeneous catalysis on metal oxide substrates such as TiO2 as well as surface growth processes in processes such as atomic and molecular layer deposition (ALD/MLD). D. A further direction concerns multi-scale of complex organic film morphologies and formation processes. We have identified opportunities to study bimolecular quenching reactions at variable concentrations as a stepping-stone to couple information about complex morphology with molecular electronic structure properties. This project continues and expands previous SNIC project on tetralith (2023/5-263)