Structures and Solvation Energies Effects Versus Temperature. An MP2 Investigations in the Framework of Cluster Model

Structures, relative stabilities, solvation enthalpies, and free energies of the $$ cluster in gas and in water phases were investigated in this work using Moller-Plesset perturbation theory (MP2) and considering a temperature range of 40-400 K. The 12 H₂O molecules are distributed between the first, second, and third solvation shells. The calculated distances $$ distances in gas phase are in good agreement with the experimental range which confirms the strong influence of long-distance interactions in cluster stabilization. Structural comparison between gas and water phases shows that the addition of the bulk solvent causes changes in the cation-water bond lengths of few hundredths of angstroms. The obtained solvation free energy of beryllium ion in water at room temperature (298.15 K) results in b - 575.1 kcal mol^-1 in very good agreement with the corresponding experimental counterpart. The computed solvation free energies increase as a polynomial function of the temperature while the change in the solvation enthalpies is found to be negligible.