A hybrid quantum mechanical molecular mechanical method: Application to hydration free energy calculations

A hybrid quantum mechanical molecular mechanical (QMMM) approach is used to study H3O+, H2O, NH4+, NH3, Cl−, HCl, F−, HF, CH3COO−, CH3COOH, Ag+ and glycine in both zwitterionic and nonzwitterionic forms in water. The free energies of hydration of these species are presented and are shown to compare favorably with experimental values. The difference in water–glycine interaction energy between the zwitterionic and nonzwitterionic forms is calculated as a lower limit and is in line with previous findings. The first theoretical examination of the Ag+–glycine complex in solution is presented.