The substitution of Cu2+ by Ag+ in hydrated Culls and (Cu-II)(3)S-3 was modeled computationally by density functional theory quantum theory of atoms in molecules, and solvent field methods. The coordination, first-shell and partly second-shell molecular structures, and thermochemical data for solvated Cu2+, Ag+, Culls, (Cu-II)(3)S-3, AgCu2S3 and their reactions were obtained. The thermochemical data showed that displacement of Cu2+ and Cu+ from Culls and (Cu-II)(3)S-3 by Ag+, while unfavorable in the gas phase, is facilitated in an aqueous environment. Several covalently bonded species were examined as intermediates in the substitution reactions.