Molecular dynamics simulation with the charge response kernel: Diffusion dynamics of pyrazine and pyrazinyl radical in methanol

The present study involves two themes. The first is to incorporate the charge response kernel ${\mathrm{(\partial Q}}_a{\mathrm{/\partial V}}_b)$ into the molecular dynamics simulation, where $Q_a$ denotes the partial charge at the site $a$ and $V_b$ the electrostatic potential at the site $b$ . The response kernel was ab initio calculated in our previous study [A. Morita and S. Kato, J. Am. Chem. Soc. 119, 4021 (1997)], and it provides a useful way to describe the polarization effect in solution, with several advantages discussed in Sec. I. The second theme is to elucidate the anomalously slow diffusion of some aromatic radicals using the above procedure. It demonstrated that the difference in the polarization effect of pyrazinyl radical (product of hydrogen abstraction) and pyrazine (parent) manifests itself in the diffusion coefficients. The analysis of the frictional force revealed the different dynamics of diffusion.