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Calculation of polymer elastic moduli using semiempirical methods
Author(s) -
Klei Herbert E.,
Stewart James J. P.
Publication year - 1986
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560300746
Subject(s) - mndo , moduli , anharmonicity , diatomic molecule , hamiltonian (control theory) , polymer , dimensionless quantity , polyoxymethylene , materials science , thermodynamics , physics , chemistry , molecular physics , quantum mechanics , mathematics , molecule , composite material , mathematical optimization
Extensional elastic moduli have been calculated for several organic high polymers based on the modified neglect of diatomic overlap ( MNDO ) Hamiltonian. Standard semiempirical methods, by application of the Born–von Karman boundary conditions, can be used to calculate heats of formation of polymer chain sections, or computational unit cells, called clusters. Unit cell heats of formation at elongated translation vectors, combined with experimental or estimated densities, allow for the calculation of elastic moduli. Two potential sources of error were identified: (a) finite geometry optimization can result in pseudorandom errors in the calculated heat of formation, and (b) anharmonic distortion can become significant at large strains. Errors due to both causes can typically be minimized if strains between 3 and 10% are selected. As expected, the calculated moduli, although higher than those observed experimentally, agree with longitudinal values for perfectly oriented systems.