Electronic structure of polystyrene: A valence effective Hamiltonian theoretical study

We describe valence effective Hamiltonian (VEH) calculations of the band structure and density of valence states of polystyrene, the prototype of pendant-group polymers. The upper two occupied bands are found to derive directly from the upper two molecular orbitals of the benzene moieties, in agreement with the molecular-ion model developed by Duke et al. For a perfectly stereoregular chain, the highest occupied band is calculated to have a width of the order of 1 eV. Taking into account solid-state effects, we simulate the theoretical UPS spectrum of polystyrene and compare it to the experimental spectrum. Provided the influence of disorder is properly considered, we obtain an excellent overall accord which permits us to easily interpret the origin of the peaks occurring in the experimental spectrum on the basis of the VEH band structure. These results indicate that the VEH technique can be applied reliably to polymers which have both saturated and unsaturated components.