FIRST-PRINCIPLES CALCULATION OF THE CONFORMATION AND ELECTRONIC-STRUCTURE OF POLYPARAPHENYLENE

In this article, an all-electron first-principles total energy calcula tion with Gaussian-type functions for the wave functions, for the exch ange correlation potential, and for the charge density has been applie d for single chains of polyparaphenylene (PPP). A local-density approx imation within a helical band structure approach has been used. The ca lculated torsional potential shows a minimum at the torsion angle of 3 4.8 degrees. The internal coordinates were optimized in the equilibriu m conformation and are in good agreement with experimental and other t heoretical results. The calculated direct band gap is 2.54 eV compared with the experimental result from UPS spectra of 3.4 eV for the gas p hase. The band structure strongly depends on the conformation which su ggests that the electronic properties can be modified in a wide range through doping or addition of side groups. (C) 1998 American Institute of Physics. [S0021-9606(98)30743-6].