Influence of solid solution formation on polarity:: Molecular modeling investigation of the system 4-chloro-4'-nitrostilbene/4,4'-dinitrostilbene

Growth-induced polarity formation in solid solutions composed of dipolar 4-chloro-4'-nitrostilbene molecules and nonpolar 4,4'-dinitrostilbene molecules was investigated by means of two molecular modeling procedures. Calculation of the mixing energy in the bulk structures predicted solid solution formation within the whole composition range. Computation of the interaction energies present at growing surfaces allowed the distribution coefficient as well as the fraction of dipoles in either the up or down orientation to be calculated by a mean-field model. Miscibility and polarity were found to vary for the faces (hkl) investigated, leading to crystals composed of sectors with different compositions and polarities. The present study highlights the fact that a solid solution crystal may not be a homogeneous entity and that surface effects arising during slow growth can have an impact on solid state properties.