The crystallization of alkali halides from aqueous solution: An application of density-functional theory

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Abstract
Density‐functional theory is applied to the problem of salt crystallization from solution and explicit results are given for model aqueous alkali‐halide systems. Both direct‐ and Fourier‐space methods of calculation are considered and it is found that only the direct (i.e., r space) method converges sufficiently rapidly to provide reliable results for ionic crystals at 25 °C. It is shown that the density‐functional method is capable of predicting crystallization, but that the solid‐state parameters and, for some salts, the crystal structures obtained are in poor agreement with experiment or computer simulations. The calculated crystal/solution coexistence concentrations are found to be extremely sensitive to the short‐range part of the interionic pair potentials. This is consistent with earlier observations that the activity coefficients of model aqueous alkali‐halide solutions are very strongly dependent upon the short‐range ion–ion interactions. Therefore, we do not believe that this sensitivity to details of the short‐range interionic potentials is an artifact of theoretical approximations, but rather a real effect significantly influencing crystallization.