Growth and dissolution mechanism at the opposite and hemihedral faces of polar crystals

Abstract

The unidirectional growth and dissolution at the opposite and hemihedral faces of the polar crystals from vapour phase is an important and unresolved problem till date. Here, we report periodic density functional total energy calculations to elucidate the mechanism of growth and dissolution at the opposite and hemihedral faces of two polar crystals, namely α-resorcinol and urea crystals from vapour phase. We employed a molecular-scale modelling based on the surface docking approach to determine the molecular attachment and detachment energies. The approach is based on the fact that polarization along the polar axis is different and hence the molecular attachment and detachment energies of molecules at these faces are different. Our results show that the phenomena of asymmetric growth and dissolution along the polar axis of α-resorcinol and urea crystals are intrinsic to the acentric crystals on which surface relaxation further enhances the asymmetry which is in agreement with the experimental observations.