Equilibrium and Growth Morphology of Oligoacenes: Periodic Bond Chains (PBC) Analysis of Tetracene Crystal

The athermal equilibrium and growth shapes of tetracene crystal were calculated, in a vacuum, by using computer codes (CSEHP, GULP, and TINKER) along with three different sets of empirical potentials (UNI, UFF, and MM3 force fields). The surface profiles were obtained by applying the Hartman-Perdok method of the periodic bond chains (PBC). The specific surface and attachment energy values were calculated, both for ideal and relaxed surface profiles. From calculations, it follows that the equilibrium shape of tetracene shows a nearly barrel habit: one form, the (001}, rules over the other ones, and several faces roughly belong to the zone axis perpendicular to the dominant form. Concerning the growth morphology, a plate like habit with the dominant pinacoid is obtained. An excellent agreement among the three force fields employed was observed. A relevant result emerging from this work is the observation that surface relaxation in general weakly affects surface and attachment energies of molecular crystals