Giovanni Ciccotti

Constrained reaction coordinate dynamics for the simulation of rare events

Abstract A computationally efficient molecular dynamics method for estimating the rates of rare events that occur by activated processes is described. The system is constrained at “bottleneck” regions on a general many-body reaction coordinate in order to generate a biased configurational distribution. Suitable reweighting of this biased distribution, along with correct momentum distribution sampling, provides a new ensemble, the constrained-reaction-coordinate-dynamics ensemble, with which to study rare events of this type. Applications to chemical reaction rates are made.

Constrained molecular dynamics and the mean potential for an ion pair in a polar solvent

Abstract A constrained molecular dynamics (MD) method for the calculation of the potential of mean force is described, and applied to study the solvent-separated and contact ion pair equilibrium in a polar solvent. The method uses holonomic constraints on the MD to fix ion pair internuclear separation. The average force exerted on the ions by the solvent is computed as a function of ion separation, and the potential of mean force follows from an integration of the mean force. The ion pair mean potential, the reaction equilibrium constant and the solvent structure in the vicinity of the ions are examined for two model solvents with differing molecular dipole moments. The relevance of this study for the dynamics of the contact ion pair-solvent separated ion pair reaction is pointed out.

Environmental Dynamics and Electron Transfer Reactions

Recent theoretical and computer simulation work on the dynamics associated with electron transfer processes in polar solvents is described. This includes solvent relaxation subsequent to photo-induced charge transfer, adiabatic electron transfer rates, and the solvent influence on the electronic states relevant to electron transfers.