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ION–SOLVENT INTERACTIONS  153

          11.  H. Ohtaki and T. Rednai, Chem. Rev. 93: 1157 (1993).
          12. Y. Marcus, Faraday Trans. 89: 713 (1993).
          13.  B. E. Conway and D. P. Wilkinson, “Evolution of Single Ion Entropies,” Electrochim. Acta
             38: 997 (1993).
          14. T. Barthel, J. Mol. Liquids 65: 177 (1995).
          15.  J. M. Alia, H. G. M. Edwards, and J. Moore, Spectrochim. Acta 16: 2039 (1995).
          16.  P. Dangelo, A. Dinola, M. Mangani, and N. V. Pavel, J. Chem. Phys. 104:1779 (1996).



         2.17. COMPUTER-SIMULATION APPROACHES TO IONIC SOLVATION

         2.17.1. General

             For about 95%  of the  history of modern  science, since  Bacon’s  work in the
         seventeenth century, the general idea of how to explain natural phenomena consisted
         of a clear course: collection of the facts, systemization of them into empirical laws,
         the invention of a number of alternative and competing intuitive models by which the
         facts could be qualitatively understood, and, finally, mathematical expression of the
         more qualitatively successful models to obtain sometimes more and sometimes less
         numerical agreement with the experimental values. The models that matched best were
         judged to describe a particular phenomenon better than the other models.
             Until the 1960s, one of the difficulties in this approach was the lengthy nature of
         the calculations  involved.  Using only mechanical calculators,  adequate numerical
         expression of a model’s prediction would often have taken an impractical time.
             Electronic calculating machines (the hardware) that can read instructions on how
         to carry out the calculations (the software) have made it much easier to select models
         that give the best prediction. However, not only has this technology transformed the
         possibilities of calculating the consequences of intuitive assumptions (reducing the
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         time needed for calculation from weeks and months to minutes and hours),  but it has
         made possible another approach toward putting experimental results into a theoretical
         framework. Instead of making up intuitive suppositions as to what might be happening
         in the system concerned, and seeing how near to reality calculations with competing
         models can come, the alternative mode is to calculate the forces between the particles
         concerned and  then to  use classical  mechanics to  calculate the  properties of the
         particles without prior assumptions as to what is happening. In physical chemistry,
         phenomena often result from a series of collisions among particles, and that is what
         can be calculated.
             Computational chemistry can be applied to all parts of chemistry, for example, to
         the design of corrosion inhibitors that are not toxic to marine life. In this section, a


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          This assumes that a program for the calculation concerned has already been written. If not, it may take an
          experienced specialist 6 months to write, and cost $50,000 to buy.
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