Ar. George et al., COMPUTATIONAL INVESTIGATION OF SURFACE STRUCTURAL RELAXATION IN CRYSTALLINE UREA, Journal of materials chemistry, 5(1), 1995, pp. 133-139
The effects of surface structural relaxation on the energetic and morp
hological properties of crystalline urea have been investigated. Speci
fically, the {001}, {110}, {200}, {101}, {(111) over bar} and {(111) o
ver bar} surfaces have been considered. Upon relaxation of the cleaved
surfaces, significant perturbations in the positions and internal geo
metries of the molecules (compared with the corresponding positions in
the bulk crystal structure) are observed. Interestingly, the {(111) o
ver bar} surface has a lower surface energy than the {111} surface, an
d thus a polar morphology is predicted. The predicted crystal shape is
compared with that observed experimentally (for crystals grown by dep
osition from the vapour phase), and reasons for discrepancies between
the calculated and experimental morphologies are discussed.