Pourbaix diagrams of alkaline earth metal elements by combination of first principles calculations and thermochemical data.

Based on first principles calculations for crystals and experimental thermochemical data for aqueous solutions and molecules, Pourbaix diagrams of alkaline earth metal systems at 298.15 K are constructed. Phonon frequencies are computed for all crystals of interests by the first principles method. Then individual contributions of zero-point energies and vibrational free energies are examined. The contribution of the zero-point energy is found to be 7-8% of the total formation free energy at 298.15 K in hydroxides, which can be ascribed to the presence of high frequency OH stretching modes. The agreements between computed and experimental Pourbaix diagrams are quite satisfactory.