The solvation free energies of ions are one of the most fundamental properties in physical chemistry and it is crucial for models of electrolyte solutions to correctly reproduce them. Surprisingly though, we still do not know what these values are for individual ions. Experimental methods can only determine these values for neutral ion pairs. Here, we use <i>ab initio</i> molecular dynamics (AIMD) simulation to calculate these energies for the lithium and fluoride ions, showing excellent experimental agreement for the lithium fluoride pair. (Figure 1) This calculation relies on accurate large-scale AIMD simulations of the air-water interface. In addition, the solvation energy is partitioned into physically intuitive contributions such as surface potential, charging and cavity terms. (Figure 2) We also present a new method to rigorously correct for the error associated with the revPBE-D3 functional by using stationary calculations at the MP2 level. Armed with these benchmark values, we can parameterize and test coarse-grained models of electrolyte solution to ensure that they accurately reproduce the free energies of ions in solution. This is significant as ion free energy changes help determine a huge range of properties such as surface forces, which are crucial for materials assembly processes in the condensed phase. The protocols developed also allow for the application of AIMD techniques to a whole new class of problems that depend on free energy changes.

Single ion solvation free energies with ab initio molecular dynamics

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.