Expanding upon our previous studies of the properties of Au complexes, we present calculations for several Hg (super 2+) species in aqueous solution and for molecular models for cinnabar. Hydration effects are treated with a combination of "supermolecule" calculations containing several explicit water molecules and polarizable continuum calculations. We focus upon the following problems: (1) calculation of the stabilities of HgL 2 , L = F (super -) , Cl (super -) , OH (super -) , SH (super -) , and CN (super -) and HgCl n (super 2-) n n = 1-4; (2) development of a molecular model for cinnabar of the form Hg 3 S 2 (SH) 2 ; and (3) dissolution or adsorption reactions using this cinnabar model. The absolute and relative formation enthalpies of the HgL 2 species can be satisfactorily reproduced at the Hartree-Fock plus Moller-Plesset second order correlation correction level using relativistic effective core potential basis sets if the hydration of neutral HgL 2 is explicitly taken into account. Evaluating the energetics for the series of complexes HgCl n (super 2-) n is more difficult, because great accuracy is needed in the large hydration energies and some of the species are highly nonspherical. The Hg 3 S 2 (SH) 2 species shows an equilibrium structure very much like that in cinnabar. The relative energetics for dissolution of cinnabar by H 2 O, H 2 S, SH (super -) , and SH (super -) +elemental S are correctly reproduced using this model molecule. Calculations on Hg 3 S 2 ClI provide a model for understanding the adsorption of I (super -) ions on cinnabar surfaces in the presence of Cl (super -) .