The project focuses on the application of computational chemistry to the design and modeling of sustainable catalysts for water oxidation. This is a key technology for the development of solar fuel devices, which, thanks to the production of hydrogen from water and sunlight, will reduce the present dependence on oil and gas supplies. The project is targeted at the main challenges of water oxidation catalysis: high activity, robustness, sustainability and modularity. A group of known catalysts, some of them assembled to photosensitizers, will be studied in detail by using state-of-the-art methods. These include DFT and TDDFT methods used in combination with implicit and explicit solvation models. Advanced tools like the AFIR (Artificial Force Induced Reaction) method and linear-scaling DFT calculations on large molecular systems will be also used. The reaction mechanisms will be determined for both productive and unproductive (deactivation) pathways. The excited states and the UV-VIS spectra of the photosensitizers attached to the catalysts will be also explored. The knowledge acquired in these studies will be exploited to design catalysts showing higher performance. These new systems will be tested in silico and developed in the laboratory by means of collaborations with experimental groups. The project funds will be used to provide the applicant with a researcher contract of four years. This will guarantee the execution of the project and improve the permanent integration prospects of the researcher at the host institution.