Influence of Formamide on the Crystal Habit of LiF, NaCl, and KI: A DFT and Aqueous Solvent Model Study

We have performed a density functional study to examine the effect of formamide on the morphology of different alkali halide (namely LiF, NaCl, and KI) crystals. The calculations were performed both in the gas phase and aqueous phase using a continuum model (COSMO/COSMO-RS). Solvation is observed to have a major effect on the interaction energies whereas the matching of the size of the additive with the neighboring ion spacing on the lattice planes of the different alkali halides is seen to be less important. The calculated results employing the slab models show that, in the aqueous phase, formamide interacts preferentially with the {111} surface of sodium chloride (Δ E = −23.8 kcal/mol for {111} vs −0.4 and −4.3 kcal/mol for {100} and {110}, respectively). This would favor the formation of octahedral-shaped crystals as reported experimentally ( Surf. Sci. 2003, 523, 307−315). On the other hand, interaction of formamide with all the surfaces of LiF are found to be repulsive in the aqueous phase while, in the case of KI, the interactions are weak (∼−2 to −5 kcal/mol) on all surfaces, i.e., no pronounced effect of formamide on morphology is expected.