Examining the influence of the [Zn(H2O)(6)](2+) geometry change on the Monte Carlo simulations of Zn2+ in water

Quantum chemical calculations have been carried out to estimate the variation in the interaction energy between one or two water molecules and the Zn2+ hydrated ion ([Zn(H2O)(6)](2+)) when the Zn-O intramolecular distance is changed. Likewise, changes in the interaction energy between a second hydration shell formed by twelve H2O and the hydrated ion when shrinking the hexahydrate have been also examined, using a previously reported hydrated ion-water potential [Pappalardo et al., J. Phys. Chem. 97, 4500 (1993)] and the Matsuoka-Clementi-Yoshimine (MCY) potential for the water-water interactions. Using these potentials and that of Clementi for the Zn2+-H2O interaction, Monte Carlo simulations have been performed using two different Zn-O distances for the first hydration shell. Results show that influence of the geometrical relaxation on the solvation energy is not large, about 2.5%. Consequences on the use of a flexible or rigid hydrated ion are discussed. (C) 1996 American Institute of Physics.