The characterization of electronic defect states of single and double carbon vacancies in graphene sheets using molecular density functional theory

Abstract

A 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 1 A g state in the smallest systems is destabilised in the extended 7a,7z-periacene system, which has the 3 B 2u 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.

Description

© 2019, © 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. cc-by

Keywords

DFT, Excited states, Periacenes, polycyclic aromatic hydrocarbons, pyrene

Citation

Pinheiro, M., Cardoso, D.V.V., Aquino, A.J.A., Machado, F.B.C., & Lischka, H.. 2019. The characterization of electronic defect states of single and double carbon vacancies in graphene sheets using molecular density functional theory. Molecular Physics, 117(9-12). https://doi.org/10.1080/00268976.2019.1567848

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