Of all the aqueous-solvated ions studied, nitrate is arguably the most abundant and important. Nitrate is a highly reactive molecule with a role in many biological processes, and nitrate is a major player in atmospheric chemistry. Consequently, the solvation and behavior of aqueous nitrate has been the subject of a great many experimental and theoretical research papers. The discussion of whether a variety of ions, particularly nitrate, prefer to reside on the surface or the interior of aqueous solutions has been ongoing for the better part of the last century.<br/><br/>The surface affinity of the nitrate ion in aqueous clusters is investigated with a variety of theoretical methods. A sampling of structures in which the nitrate ion is solvated by 32 water molecules is optimized using second order Møller-Plesset perturbation theory (MP2). Four of these MP2 optimized structures are used as starting points for fully ab initio molecular dynamics simulations at the dispersion corrected restricted Hartree-Fock (RHF-D) level of theory. The nitrate ion solvated by 16, 32, and 64 water molecules is also investigated with umbrella sampling molecular dynamics simulations using QM/MM methodology, where the nitrate ion is modeled with MP2 and the water molecules are described using either the non-empirical effective fragment potential (EFP) or the empirical TIP5P potential. The turning point between surface and interior solvation of the nitrate ion is predicted to lie around a cluster size of 64 water molecules.

<i>Ab initio</i> investigation of the aqueous solvation of the nitrate ion

251st National Meeting (2016)

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Ab initio investigation of the aqueous solvation of the nitrate ion