QUASI-PARTICLE SPECTRA OF TRANSPOLYACETYLENE

A first-principles calculation to determine the electronic properties of trans-polyacetylene using Hedin's GW approximation for the self-ene rgy is described. To our knowledge this work is the first application of the GW method to a quasi-one-dimensional system. The zeroth-order a pproximation is used to initialize the calculation with the self-energ y described by the Hartree-Fock exchange interaction. To include elect ron exchange and correlation beyond Hartree Fock, the first-order (GW) approximation for the self-energy is adopted. Now the self-energy is energy dependent and is described by the single-particle Green's funct ion (G) and the screened Coulomb interaction (W). For screening the Co ulomb potential the complete wave number and frequency-dependent diele ctric response tensor, within the random phase approximation, is emplo yed. The GW calculation is carried to self-consistency, By implementin g the GWA, the Hartree-Fock minimum band gap is reduced by 68% and fal ls within the experimentally observed range. The optical reflectance a nd electron-energy-loss function, calculated with local field and life time effects, are presented and compared with experiment.