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

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Abstract
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.