Ion solvation free energy calculations based on first-principles molecular dynamics thermodynamic integration.

The article focuses on a first-principles thermodynamic integration (TI) approach for accurately calculating ion solvation free energies in liquid water, addressing challenges in existing models due to unphysical intermediate states and entropy extraction difficulties. The method decomposes ion dissolution into three sub-processes—cavity creation, ion addition via a two-system density functional theory (DFT) calculation with weighted averaging, and cavity elimination—enabling stable ab initio molecular dynamics simulations without empirical parameters. Applied to Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ ions, the calculated solvation energies closely match experimental values within uncertainties, with standard deviations from molecular dynamics fluctuations below 0.06 eV. Additionally, the approach yields solvation voltages consistent with experimental electrode potentials, offering a robust and theoretically grounded alternative to implicit, explicit, and hybrid solvent models for studying ion solvation in electrochemical contexts.