Development of generation of large-male potential energy surfaces num local interpolation and molecular mechanics

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In large scale systems, so called QM/MM methods have been employed in the quantum chemistry society and tens of trajectories (even only one trajectory) sometimes have been employed to extract the picture of reaction mechanism. However, it is still difficult for us to obtain the number of trajectories which is statistically significant because potential energy calculations are time consuming. The statistically significant result may be drastically different from the picture that was obtained from tens of trajectory calculations. Thus, it is desirable to construct a method to evaluate potential energy surface fast. We attempted to combine a local interpolation scheme, IMLS/Shepard scheme, and molecular mechanics, but the attempt is still under way.Thus, we have undertaken a direct dynamics for a biomolecule, retinal, instead. We described the dynamics of retinal using Zhu-Nakamura formula for non-adiabatic transitions from the first (photo) exited state to the ground state. We treated all the degrees of freedom in our direct dynamics although we originally planned to describe small number of degrees of freedom icing IMLS/Shepard scheme and the other degrees of freedom using molecular mechanics. We have found that retinal (at least in gas phase) experiences two-step relaxation after the deexcitation through non-adiabatic transition.Also, we have applied our IMLS/Shepard scheme to the O+HCl system. Large scale trajectory calculations using three potential energy surfaces have been carried out to obtain reactive differential cross sections and the results are in agreement with experiment We have found that the dynamics is determined by that in the ground state although the two excited states are in a relatively low energy region.