Quantum chemical methods for the investigation of photoinitiated processes in biological systems: Theory and applications

With the advert of modern computers and advances in the developmentof efficient quantum chemical computer codes, the meaningful computation of large molecular systems at a quantum mechanical level became feasible. Recent experimental effort to understand photoinitiated processes ion biological systems, for instance photosynthesis or vision, at a molecular level also triggered theorethical investigations in this field. In this Minireview, standard quantum chemical methods are presented that are applicable and recently used for the calculation of excited states of photoinitiated processes in biological molecular systems. These methods comprise configuration interaction singles, the complete active space self-consistent field method, and time-dependent density functional theory and its variants. Semiempirical approaches are also covered. Theirr basic theorethical concepts and mathematical equations are briefly outlined, and their properties and limitations are discussed. Recent successful applications of the methods to photoinitiated processes in biological systems are described and theorethical tools for the analysis of excited states are presented.