Theoretical study of proton-transfer energy surfaces in small water clusters and cubic ice

The energetics of proton transfer in water clusters consisting of two to six molecules and in cubic ice was analyzed in detail using both Hartree Fock and gradient-corrected density functional theory. Since the energy of the ion-pair structure created by proton transfer is always higher than that of the neutral water structure grid calculations and constrained geometry optimization are needed. In the case of cubic ice various arrangements of the hydrogen atoms on a fixed oxygen lattice were investigated. In this system proton transfer leads to the creation of ionic point defects which are saddle points on the potential energy surface.