Multiple steering molecular dynamics applied to water exchange at alkali ions

The novel fast-growth or multiple steering molecular dynamics (MSMD) technique has been recently developed by Jarzynski to calculate free energy profiles along general transformation pathways (Phys. Rev. Lett. 1997, 78, 2690-2693; Phys. Rev. E 1997, 56,5018-5035).(1,2) Here, we apply this approach to calculate free energy barriers involved in the water exchange reaction of Na+ and K+ in aqueous solution. We investigate the influence of the key parameters of the MSMD simulations-the steering velocity, the sampling of the initial configurations, and the force constant-on the free energy. furthermore, we use this approach to describe energetical and structural features of the water exchange reaction of Na+ and K+ in aqueous solution. The MSMD technique turns out to be an efficient and fast convergent tool to enhance the sampling of rare chemical events with-the help of nonequilibrium forces.