Theory of Chemical Dynamics

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William Miller of the University of California, Berkeley is supported by an award from the Chemical Theory, Models and Computational Methods program to explore new semiclassical initial value representation approaches for treating electronically non-adiabatic processes, i.e., those involving molecular dynamics on several potential energy surfaces (electronic states). The Meyer-Miller-Stock-Thoss representation of the vibronic Hamiltonian provides one well-established way for doing this, and more efficient ways of carrying out calculations within this framework are pursued. A more ambitious but less well established approach, that shows great promise, introduces the classical description of the electronic degrees of freedom at a more fundamental level, that of the creation/annihilation operators of the individual fermionic states. This formulation is being pursued to see if the initial very promising performance it has demonstrated is maintained more generally.Electronically non-adiabatic processes underlie a number of applications that are crucial for many technologies of current importance. These include photo-voltaic processes relevant to solar-to-electric energy conversion, in both inorganic nano-materials and in photosynthetic systems, and the field of "molecular electronics", e.g., the transmission of electrons through various molecular structures that are junctions between electrodes. Development of theoretical descriptions that allow one to treat non-adiabatic processes within the framework of classical molecular dynamics simulation methodology will make it feasible to carry out such calculations for much more realistic molecular models and thus interact more fruitfully with experimental work in these areas.