  We combine a GW approach and ab initio Molecular Dynamics (AIMD) simulations
to study the impact of thermal effects on transport gap in solid pentacene
(C22H14). The dynamic disorder induced by thermal fluctuations is simulated by
AIMD, providing the ensemble-averaged density of states (DOS) near the band
gap. The GW corrected DOS, averaged over hundreds of snapshots from AIMD
simulation containing disordered structures indicates that the edge-to-edge
transport gap is 2.1+/-0.04 eV, reduced by ~0.1 eV in contrast to the static 0
K GW calculation. The peak-to-peak gap is found to be 2.7eV in excellent
agreement with experiment after corrections for the surface and the
Frank-Condon effects and providing fully ab initio agreement with experiment
where previous theory required ad hoc Gaussian broadening and temperature
corrections.
