Equilibrium and Growth Morphology of Oligothiophenes: Periodic Bond Chain Analysis of Quaterthiophene and Sexithiophene Crystals

The athermal (T = 0 K) equilibrium and growth crystal shapes of two members of the oligothiophenes series, namely, quaterthiophene and sexithiophene, were simulated in vacuo by using the UNI and UFF empirical potentials. By applying the Hartman–Perdok method of the periodic bond chains (PBC), the surface profiles were obtained, providing the specific surface and attachment energy values, both for bulk-like and relaxed surfaces. Calculations demonstrate that surface relaxation weakly affects surface and, even more, attachment energies of such semiconductor molecular crystals. The two phases show analogous features: barrel-like equilibrium shapes for both quaterthiophene and sexithiophene, and plate-like growth shapes, in particular, in the sexithiophene case.