Mechanical properties and force field parameters for polyethylene crystal

Crystal structures, phonon dispersion relations, and elastic constants of polyethylene crystal are calculated by using a new force field where the van der Waals parameters are selected on the basis of comparing these properties with experiment. The cell parameters and atomic coordinates are optimized simultaneously, and elastic constants and phonon bands are calculated by using analytic second derivatives at the optimized structure. Yield stresses and surface energies are obtained from calculations of the stress-strain relations in directions perpendicular to polymer chains.