An MO study on ~(13)C NMR chemical shift and the electronic structure of a three-dimensional polymer crystal by ab initio tight-binding MO theory I.Polyethylene crystal

摘要

Formulae for calculating the NMR chemical shift of a three-dimensional (3D) polymer crystal were derived by a combination of ab initio tight-binding MO theory and the sum-over-states method of the chemical shift theory. This formalism was applied to the calculation of the ~(13)C NMR chemical shift of 3D polyethylene chains in the orthorhombic and the monoclinic crystal-lographic forms by using the STO-3G minimal basis set. The effects of inter- and intra-chain interactions on the ~(13)C NMR chemical shift and the band structure were evaluated with a change by means of the a and c axes and the b axis in the lattice constants. THe calculated results explain reasonably the experimental data.