The Importance of Thermodynamic Quantities for the Determination of the Unknown Conformation: Ab initio Studies of K+(H2O)3

摘要

The structures, the energetics, and the spectra of K+(H2O)3 have been studied at HF and MP2 levels with the basis set of triple-zeta plus two sets of polarization functions (TZ2P) for water molecules. Two structures considered are 3+0 (D3), and 2+1 (C2v). The 2+1 (C2v) has two hydrogen bonds between the primary hydration and the secondary hydration shell water molecules. They have similar binding energy and enthalpy. The most stable conformation of K+(H2O)3 is entropy driven as shown in Na+(H2O)5 and in Na+(H2O)6 cases. The 3+0 (D3) conformation is the most stable at 298 K and at 1 atm, based on Gibbs free energy changes (ツGr). The thermal contributions to the enthalpy and the Gibbs free energy are corrected for the low frequency modes. The corrected ツGr is in good agreement with the experimental value. Vibrational frequencies of two conformations are revealed as their characteristics.