Ab initio molecular dynamics calculations of ion hydration free energies

We apply ab initio molecular dynamics (AIMD) methods in conjunction with the thermodynamic integration or " λ -path" technique to compute the intrinsic hydration free energies of Li+, Cl-, and Ag+ ions. Using the Perdew-Burke-Ernzerhof functional, adapting methods developed for classical force field applications, and with consistent assumptions about surface potential (φ) contributions, we obtain absolute AIMD hydration free energies (Δ Ghyd) within a few kcal/mol, or better than 4%, of Tissandier 's [J. Phys. Chem. A 102, 7787 (1998)] experimental values augmented with the SPC/E water model φ predictions. The sums of Li+ / Cl- and Ag+ / Cl- AIMD Δ Ghyd, which are not affected by surface potentials, are within 2.6% and 1.2 % of experimental values, respectively. We also report the free energy changes associated with the transition metal ion redox reaction Ag+ + Ni+ →Ag+ Ni2+ in water. The predictions for this reaction suggest that existing estimates of Δ Ghyd for unstable radiolysis intermediates such as Ni+ may need to be extensively revised. © 2009 American Institute of Physics.