Abinitioinvestigation of the electronic properties of planar and twisted polyparaphenylenes

Abstract

Ab initio band-structure calculations are carried out on stereoregular polyparaphenylene at the Hartree-Fock level of approximation using the split-valence 3-21G basis set. We investigate the effects due to the torsion angle between adjacent phenyl rings upon the ionization energies and bandwith values, as well as upon the density of states and the uncoupled Hartree-Fock longitudinal polarizability per unit length. From the bandwidth values, it is inferred that solid polyparaphenylene is better represented by the 22.7°twisted structure, whereas the torsion angle of polyparaphenylene in the gas phase should be roughly 40°. As for polypyrrole, polyfurane, and polythiophene, the highest occupied crystalline orbital is the most contributing band.

First-principles calculation of the conformation and electronic structure of polyparaphenylene

“…Correlation corrections reduce the valence and conduction bandwidths to 4.12 and 5.22 eV, respectively. 33 The restricted HF calculation by Champagne et al 37 gave a valence bandwidth of 4.45 eV which is similar to the results of Ladik et al The ultraviolet photoelectron spectroscopy ͑UPS͒ study carried out on solid and gaseous sexiphenyl reported for the valence bandwidths values of 3.5 and 2.9 eV, respectively. 24 Of course to obtain an estimate of mobility, one has to take into account interchain hoppings which may even be dominant.…”

“…Our LDA result for the ionization potential is 4.93 eV whereas the XPS 23 37 using a split-valence 3-21G basis set predicted an ionization energy of 7.16 eV.…”

“…Each degenerate energy level in benzene will split into two nondegenerate levels, one belonging to the a 2 representation in C 2v and the other belonging to the b 2 representation. As Champagne et al 37 have noted, the a 2 state will have no contribution from the atoms at the end points of the bonds between phenyl rings. Within a nearestneighbor tight-binding model, this a 2 band would show a total lack of dispersion, but with longer-range contributions included in the first-principles calculations we find that the interactions between monomers cause the band to be weakly bonding with it rising in energy slightly from Brillouin zone center to zone edge.…”

“…35 They have calculated the self-energy using second-order Mo "ller-Plesset perturbation ͑MP/2͒ theory. 36 More recently, Champagne et al 37 carried out another ab initio HF study of the electronic properties of planar and nonplanar PPP and made an analysis of the polarizability of PPP as well as the inter-ring torsion effects upon the polarizability. Ambrosch-Draxl et al 38 used a first-principles local density approximation ͑LDA͒ with a full potential linearized augmented plane wave ͑LAPW͒ as well as a pseudopotential method to calculate torsional angles of 22.7°in a single PPP chain and 17°in crystals.…”

Density functional calculations on the structure of crystalline polyethylene under high pressures

“…In each unit cell, there are four (CH) 2 groups situated in two polymer chains. The LDA and GGA optimized geometrical parameters, including the bond lengths, the bond angles and the setting angle of the chain as well as the lattice vectors are listed in Table I together with the experimental results [33][34][35] and the other theoretical predictions 36,37,21,24 for both the single chain and the crystalline system. For reasons of numerical stability that will be discussed below, the GGA geometry is actually obtained at a pressure of 0.1 GPa which is sufficiently small in comparison with the pressure steps of 2 GPa used in this article.…”