The characterization of electronic defect states of single and double carbon vacancies in graphene sheets using molecular density functional theory |
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Authors: | Max Pinheiro Jr Daniely V V Cardoso Adélia J A Aquino |
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Institution: | 1. Departamento de Química, Instituto Tecnológico de Aeronáutica, S?o Paulo, Brazil;2. Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX, USA;3. School of Pharmaceutical Sciences and Technology, Tianjin University, Tianjin, People’s Republic of China;4. Institute for Theoretical Chemistry, University of Vienna Vienna, Austria |
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Abstract: | ABSTRACTA detailed picture of the electronic states manifolds of single- and double-vacancy defects in molecular models of graphene based on polycyclic aromatic hydrocarbons (PAHs) is presented. DFT calculations using various density functionals including long-range corrected ones have been performed for pyrene, circumpyrene and 7a,7z-periacene. It has been found for pyrene defect models that DFT results reproduced well the set of closely-spaced singlet and triplet states predicted by the CCSD(T) and previous MRCI?+?Q calculations, indicating the applicability of DFT for accessing the excited states manifolds also for larger graphene models. For the single-carbon vacancy defect, all structures have a triplet ground state. As expected, in the largest system, 7a,7z-periacene-1C, the lowest lying states are much closer in energy. For all double-vacancy defect structures, a significant rearrangement of the electronic states with increasing size of the sheet is observed. The closed-shell 1Ag state in the smallest systems is destabilised in the extended 7a,7z-periacene system, which has the 3B2u state as the ground state. As observed for the single-vacancy defect, the lowest lying states are closer in energy for the larger systems, since there are more π orbitals close in energy available. For all states, the formation of the bridging bonds for the double vacancy leads to distances shorter than for the single vacancy defect indicating a larger rigidity of the former structure which does not allow stronger distortions. |
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Keywords: | Excited states polycyclic aromatic hydrocarbons pyrene Periacenes DFT |
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