Partenaires et organisations internationales
(Anglais)
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BE, BG, CH, CZ, DE, DK, ES, FI, FR, HU, IE, IT, NL, NO, PL, PT, RS, SE, SK, UK
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Résumé des résultats (Abstract)
(Anglais)
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The proposed project integrated in CODECS aims at the development, distribution and applications of reliable methods for predicting the nature of the charge carriers in conducting organic polymers (COPs). COPs are promising materials for electronic applications such as field effect transistors, light emitting diodes and photovoltaic cells. Despite numerous computational studies performed on p-doped oligothiophene model systems, the exact nature of the charge carriers with respect to increasing the chain length in these systems remains elusive. In particular, short chains are commonly described as a bipolaron (i.e. charge localizes on a few atoms), but there is no general consensus on the chain length for which the bipolaron to polaron pair (i.e. charges located at each end of the molecule) transition occurs with results ranging from 4 to 14 monomers. The accurate description of large chains of oligothiophenes is indeed very challenging for electronic structure methods. A strong multireference character characterizes these systems but their large size (up to 20 monomer units/120 ?-electrons) precludes the use of high-level multireference ab initio methodologies. Kohn-Sham (KS) density functional theory (DFT) mimics some of the effects of static correlation and appears as the only alternative for treating such systems. However, standard approximations are known to suffer from the delocalization and the spin-polarization error that manifest themselves into systematic underestimation of singlet-triplet energy differences and inaccurate bond-length alternations. The treatment of excited states is affected by related errors within the time-dependent DFT framework. We here propose to devise methodologies that would enable the unambiguous description of the charge carrier's nature in doped oligothiophene dications. This research program evolves along two specific aims that are: (i) the development of a density matrix renormalization group (DRMG) protocol to achieve quantitative results for the energies of large-sized ?-conjugated molecules and gauge the performance and reliability of modern density functionals; and (ii) the application and expansion of an innovative scheme to establish key structure-property relationships associated with the extent of ?-conjugation in conductive oligothiophenes and their derivatives. We believe that the fundamental insights and knowledge gained during this project can have a serious impact in the field organic electronic. In particular, the question of their interpretation in terms of bipolaronic or polaron pair electronic structure should be solved unambiguous. While we will benefit from the expertise of our collaborators, the schemes delivered by our two specific aims will provide a new set of information that should be of great use to the computational chemistry community.
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