Journal
JOURNAL OF PHYSICS-CONDENSED MATTER
Volume 27, Issue 11, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0953-8984/27/11/113204
Keywords
exciton dispersion; molecular solids; Bethe-Salpeter equation
Categories
Funding
- Marie Curie FP7 Integration Grant within the 7th European Union Framework Programme
- GENCI [544]
- European Research Council Advanced Grant DYNamo [ERC-2010-AdG-267374]
- Spanish Grant [FIS2013-46159-C3-1P]
- Grupos Consolidados UPV/EHU del Gobierno Vasco [IT578-13]
- European Community FP7 project CRONOS [280879-2]
- COST Actions [CM1204, MP1306]
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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.
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