Exciton dispersion in molecular solids.
The investigation of the exciton dispersion (i.e. the exciton energy dependence as a function of the momentum carried by the electron-hole pair) is a powerful approach to identify the exciton character, ranging from the strongly localised Frenkel to the delocalised Wannier-Mott limiting cases. We illustrate this possibility at the example of four prototypical molecular solids (picene, pentacene, tetracene and coronene) on the basis of the parameter-free solution of the many-body Bethe-Salpeter equation. We discuss the mixing between Frenkel and charge-transfer excitons and the origin of their Davydov splitting in the framework of many-body perturbation theory and establish a link with model approaches based on molecular states. Finally, we show how the interplay between the electronic band dispersion and the exchange electron-hole interaction plays a fundamental role in setting the nature of the exciton. This analysis has a general validity holding also for other systems in which the electron wavefunctions are strongly localized, as in strongly correlated insulators.
Nano-Bio Spectroscopy group, Universidad del País Vasco, CFM CSIC-UPV/EHU-MPC and DIPC, E-20018 San Sebastián, Spain. European Theoretical Spectroscopy Facility (ETSF.
Pierluigi
P
Cudazzo
Francesco
F
Sottile
Angel
A
Rubio
Matteo
M
Gatti
D065966:Absorption, Physicochemical; D004583:Electrons; D008958:Models, Molecular; D055620:Optical Phenomena; D011083:Polycyclic Compounds / Q000737:chemistry*; D011789:Quantum Theory
D011083:Polycyclic Compounds