Calculation of minimum potential energy of folds and kinks in polyethylene crystals

We have performed calculations of potential energy minima for the possible conformations of folds and kinks in a polyethylene crystal. Unlike previous work, the calculations take into account the possibility of coupled variations of internal rotation angles as well as of bond angles in the search for energy minima. The conformations of minimum energy found by us for tight folds in the 200 and 110 planes of polyethylene structure have energies of the order of 3 and 4 kcal/mole, respectively, less by a factor of say 2.5 than the figures obtained by previous authors, even when the earlier results were recalculated with our “softer” energy functions. Possible conformations for a “Reneker kink” have also been calculated; their energy turned out to be of the order of 7 kcal/mole. In all cases, a wide variety of geometrical models is almost isoenergetic in the neighborhood of the conformations studied.