Parameterization and validation of solvation corrected atomic radii

The use of correct ion radii is essential for the calculation of free energies of hydration using continuum models. A simple method for the fitting of the ion radii for ions in aqueous solution, which is a consistently difficult problem for implicit solvent models, is described. A new set of ionic radii based on experimental ionic hydration free energies for use in the integral equation formalism of polarizable continuum model (IEFPCM) is derived using B3LYP calculations with a 6-31 l++g basis set for Li, Na, K, Be, Mg, and Ca and a SDD basis set for all other metals. The new radii reproduce the experimental stability constants of metal ions and their pyridine, 2,2'-bipyridine, and 1,10-phenanthroline complexes in aqueous solution significantly better than the results obtained using the default UAHF ion radii. The standard deviation (SD) of binding free energies between the calculations and experiments for the metal-ligand complexes in aqueous solution is 3.7 kcal/mol, while the mean unsigned error (MUE) is 3.1 kcal/mol. These results improve on the standard UFF radii for metal atoms, in which the MUE and the SD are 30.4 and 16.9 kcal/mol, respectively. The new ionic radii greatly improve the computational tools for the study of a variety of metals with ligands such as pyridines or calixarenes, which have found significant interest in materials science and for the removal of toxic metals.