Generalized Langevin dynamics simulation of activated processes in solution: Ion pair interconversion in water

The association–dissociation processes for Na+–Cl−, Na+–Na+, and Cl−–Cl− ion pairs in water are studied by generalized Langevin dynamics (GLD) simulation. The required solvent averaged interionic potentials and time-dependent friction coefficients were obtained previously from molecular dynamics (MD) calculations explicitly including the solvent particles. The reliability of the method is checked by comparing the GLD results for the Na+–Cl− ion pair with those obtained from full deterministic MD. The reactive flux method has been employed to compute the transmission coefficients and to study dynamic properties of activated trajectories. The results have been compared with theoretical predictions. The influence of the friction kernel has been investigated considering different models for the time-dependent friction coefficients. The mean first passage time for the dissociation process has also been calculated from GLD simulations.