Energetics during proton transfer process in hydrated zundel ion complex

Zundel ion (H5O2+) is one of the two important structures formed during the proton transfer process in aqueous system. This work reports microsolvation of Zundel ion using density functional theory based B3LYP method with aug-cc-pVTZ basis set. Interaction of Zundel ion with four water molecules in its first solvation shell is studied using many-body analysis approach. A change in many-body energies and their contribution to the binding energy of a complex during the proton transfer process from donor to acceptor water molecule in Zundel ion-4H(2)O complex is obtained. For the hydrated Zundel ion complex, the contribution from total two-body, three-body, four-body, five-body, and relaxation energy to the binding energy is 84.7, 14, 6.87, 1.6, and 4%, respectively, at B3LYP/aug-cc-pVTZ level. Relaxation energy and total five-body energy have repulsive contribution to the binding energy of a hydrated Zundel ion complex. It is found that the relaxation energy and binding energy of a Zundel-4H(2)O complex is the maximum and minimum, respectively, when a shared proton is at equal distance from oxygen atom of donor and acceptor water molecules. A significant change in two-body, three-body, and four-body energies for which Zundel ion is one of the many-body terms is observed during the proton transfer process. A change in total two-body, total three-body, total four-body, and relaxation energy is about 2.6, 1.8, 0.4, and 1.1%, respectively, during the proton transfer process. A change in two-body, three-body, and four-body interaction energies between water molecules is very small during the proton transfer process. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012