Contributions from dispersion and born self-free energies to the solvation energies of salt solutions

M. Boström*, B. W. Ninham

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    53 Citations (Scopus)

    Abstract

    That the Born theory provides an accurate means of calculating solvation energies of ions in water has been demonstrated by Rashin and Honig (Rashin, A. A.; Honig, B. J. Phys. Chem. 1985, 89, 5588). They could fit the experimental solvation energies of a number of salts nicely by a simple increase of 7% in the expected radii of all ions. However, as we demonstrate herein, there is an important previously ignored contribution due to the ionic dispersion self-free energy. The ionic parameters necessary to estimate the different contributions to solvation energy are the ionic radii, the ionic polarizabilities, and the ionization potentials. Whereas the polarizabilities and ionization potentials of a number of salts have recently been derived ab initio (in both vacuum and water), the appropriate choices of radii are less well-known. We pursue two different approaches to assign the ionic radii. In the first approach, we find that an increase of all expected radii by 23% gives reasonable agreement between theory and experiment (to within 6%). In the second approach, we increased the expected radii of six ions separately (10-30%) to obtain a best fit for the nine salts investigated. In this second approach, the deviations between theory and experiment were less than 0.1%. The essential point is that a proper theory must include contributions from both electrostatic (Born) and electrodynamic (dispersion) self-free energies.

    Original languageEnglish
    Pages (from-to)12593-12595
    Number of pages3
    JournalJournal of Physical Chemistry B
    Volume108
    Issue number33
    DOIs
    Publication statusPublished - 19 Aug 2004

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