Density functional study of polypropylene and its submolecules

Previous density functional (DF) calculations of the structures of small hydrocarbon molecules (CH, CH2, C2H2, C2H4, C3H6, C3H8) have been extended to larger systems. The structure of a single chain of isotactic polypropylene (it-PP) has been optimized, and calculations have been performed for smaller molecules with closely related structures (propane C3H8, several conformers of isopentane C5H12, and 2,4,6-trimethyl heptane C10H22) using both local spin density (LSD) and non-local (gradient-corrected) energy functionals. The pronounced transferability of the local structural parameters between C5H12, C10H22 and it-PP suggests that the energy surfaces calculated for molecules with five carbon atoms should provide a very good representation of the local energy variations in much larger systems. (C) 1997 American Institute of Physics.