The modulus and strain-dependent frequency spectrum of polyethylene have been computed from a cluster of C6Hlz units using the semi-empirical AM 1 Hamiltonian and unrestricted Hartree-Fock wavefunctions. The computed modulus substantially exceeds experimental values, a result which derives from neglect of electron correlation in the calculations. Good qualitative and quantitive agreement with reported strain-dependent frequencies is found, suggesting that the method describes cubic anharmonicity in the bonding while systematically overestimating components of the Hessian.
Посилання на статтю:
Electronic structure and properties of strained polymers: 1. Methods for polyethylene / James R. Shoemaker, Thomas Horn and Peter D. Haaland // Polymer. – 1992. – Vol 33. – P. 3351-3356.