Abstract
Abstract Earlier estimates for the Young's modulus of polyethylene based on the AM1 semi-empirical molecular orbital method were 15% larger than the largest experimental value. Neglect of electron correlation in the single determinant wavefunction for polyethylene leads to a Hessian matrix which is too stiff. Here we apply the biased Hessian approach of Dasgupta and Goddard1 to the polyethylene chain at equilibrium and under tensile and compressive strain. The chain modulus is 340 GPa with the biased Hessian, in agreement with extant experimental results. Although the variation of the vibrational spectrum with strain is reduced with biasing, the stress-dependence of vibrational frequencies is unchanged.
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