  Vibronic coupling constants in the monoanionic, trianionic, and excited
states of picene are evaluated from the total energy gradients using the
density functional theory. Employing the calculated vibronic coupling constants
in the excited state of the neutral molecule, electron energy loss spectrum
(EELS) is simulated to be compared with the experimental spectrum. The
calculated vibronic coupling constants are analyzed in terms of the vibronic
coupling density which enables us to analyze vibronic couplings based on the
relation between the electronic and vibrational structures. The vibronic
coupling constants reported by Kato et al. [J. Chem. Phys. 116, 3420 (2002) and
Phys. Rev. Lett. 107, 077001 (2011)] are critically discussed based on the
vibronic coupling density analysis.

Chemical Physics