New Computational Methods for Quantum Dynamics of Large Systems

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Going beyond the Born-Oppenheimer approximation and classical description of the nuclear motion becomes increasingly important for advancing our understanding and ability to control photochemical processes in biological and artificial systems of technological importance. Usually, photochemistry involves more than one electronic state and the well developed apparatus of Born-Oppenheimer molecular dynamics is not applicable because the nuclear motion involves switching between multiple electronic states. In many cases, electronic degrees of freedom are not the only quantum components and neglecting zero-point motion, tunneling, quantized energy levels and coherent energy transfer can cause severe discrepancies between theory and experiment. There is an increasing number of examples where quantum effects have been observed in large biological molecules like rhodopsin and bacteriorhodopsin. To obtain deeper understanding of these observations computational input is crucial. Unfortunately, quantum mechanical laws can be practically simulated for only relatively small systems. Thus, it is paramount to extend further computational techniques that would include important quantum effects in realistic simulations. The main premise in such undertaking is that it is still possible to derive a relatively small set of collective degrees of freedom whose dynamics has highly entangled quantum character while dynamics of other degrees of freedom is simpler and can be modeled with less computationally demanding approaches. In this work we would like to formally develop these ideas in order to obtain qualitative and quantitative tools for computational modelling of quantum phenomena in various photo-active proteins.