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 develop new, simple and computationally efficient approaches to studying electronically nonadiabatic chemical processes. Such processes occur when there is a coupling between the motion of the atomic nuclei, for example molecular vibrations, and motion of the electrons. They involve transitions between different electronic states, for example, the ground (lowest energy) state and a state in which the electrons are excited. These processes have relevance for many important technological applications 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. Although nonadiabatic processes are inherently quantum mechanical, Miller and his group have found that they may be modeled by a simple and purely classical treatment of the coupled dynamics. The goal is to have an approach that can be integrated into large scale simulations of realistic systems with many degrees of freedom. The PI has contributed broadly to the training of many in the field and the long term scientific impact of this work is expected to be significant.Miller and his research group continue the development of a purely classical approach to treating electronically nonadiabatic processes, building on the symmetrical quasiclassical procedure (SQC) which "quantizes" both the initial and final electronic action variables in an equivalent fashion, thus insuring microscopic reversibility. The method has its roots in the much earlier Meyer-Miller (MM) and Miller-McCurdy (MM) representations of electronic degrees of freedom in terms of classical action-angle variables. Recent applications have given encouraging results for benchmark models. The goal of the current research is to explore a range of possibilities for further developments of the SQC/MM methods.