Solvation dynamics in polar solvents studied by means of RISM/mode-coupling theory.

The extended reference interaction site model (RISM) theory coupled with the generalized Langevin/mode-coupling theory (MCT) is applied to the investigation of solvation dynamics in polar solvents. The RISM/ MCT framework used in this paper significantly upgrades the previous report by Nishiyama and co-workers [Nishiyama, K.; et al. J. Chem. Phys. 2003, 118, 2279.] for the calculation of the solvation response function, Ss(t). This function is experimentally observable from dynamic Stokes shift measurements, for example. Ss(t) obtained by RISM/MCT relaxes with an initial Gaussian decay followed by damped oscillation, which is in accordance with experimental results or molecular dynamics simulations published elsewhere. Ss(t) is then decoupled into the acoustic and optical modes of solvent, which indicate the translational and rotational motions of solvent, respectively. The majority (> 90%) of Ss(t) is explained by the optical mode, whereas the slower acoustic mode also plays an important role. Resultingly, RISM/MCT is shown to be an appropriate theoretical methodology to capture a molecular view of solvation dynamics, without assuming any empirical parameters.