Hydrogen bonded hydrated Hydronium and Zündel ion complexes

Two protonated water complexes, the hydrated hydronium ion and hydrated Zündel cation, are optimized using MP2 and density functional theory methods with different exchange and correlation functionals with an aug-cc-pVTZ basis set. A many body analysis approach is used to study the nature of various interactions between different molecules in a complex and their contribution to the binding energy of a complex. Shifts in vibrational frequencies are studied. Many-body analysis shows that not only two body but higher body energies also contribute significantly to the binding energy of a complex. Though the trend in interaction energies is similar for various functional in density functional theory, the functional affects various interaction energies in these complexes. The three hydrogen bonds in hydrated hydronium ion complexes are of equal length whereas the six hydrogen bonds in hydrated Zündel ions are not. The MPWPW91 and BLYP functionals give the shortest and longest hydrogen bonds respectively in hydrated hydronium ion complexes.