Electron Transfer (ET) reactions play a vital role in a variety of crucialbiological processes such as immune response, nitrogen fixation,respiration and photosynthesis. The latter, in particular has attracted acontinued interest, as photosynthesis constitutes the main energy sourceof our biosphere. A detailed understanding of the involved molecularmechanisms is thus of prominent interest both from a fundamental point ofview as well as for the potential design of highly efficient bioinspiredoptoelectronic devices and solar cells. Marcus theory has provided an excellent overall understanding of electrontransfer processes but it does not provide a description of thesereactions at the atomic level. Molecular dynamics (MD) simulations are inprinciple capable of supplying this information but due to the fact thatMD simulations of ET processes constitute a supreme theoretical challengeessentially no atomistic in situ simulations of ET reactions have beenperformed so far. The main objective of SNF project 200020-108063 is the development andapplication of suitable computational methods for first-principles-basedmixed quantum mechanical-molecular mechanical (QM/MM) simulations ofelectron transfer processes in biological systems.