Structural relaxations in electronically excited poly(para-phenylene)
  Structural relaxations in electronically excited poly(para-phenylene) are studied using many-body perturbation theory and density-functional-theory methods. A sophisticated description of the electron-hole interaction is required to describe the energies of the excitonic states, but we show that the structural relaxations associated with exciton formation can be obtained quite accurately within a constrained density-functional-theory approach. We find that the structural relaxations in the low-energy excitonic states extend over about 8 monomers, leading to an energy reduction of 0.22 eV and a Stokes shift of 0.40 eV. 
Emilio Artacho (1), M. Rohlfing (2), M. Cote (3), P. D. Haynes (1), R.   J. Needs (1) and C. Molteni (4) ((1) University of ...