# Publication: Singlet-triplet (S0âT1) excitation energies of the [4Ãn] rectangular graphene nanoribbon series (n=2-6): A comparative theoretical study

All || By Area || By YearTitle | Singlet-triplet (S0âT1) excitation energies of the [4Ãn] rectangular graphene nanoribbon series (n=2-6): A comparative theoretical study |
---|---|

Authors/Editors* | S Rayne, K Forest |

Where published* | Computational and Theoretical Chemistry |

How published* | Journal |

Year* | 2011 |

Volume | 977 |

Number | |

Pages | 163-167 |

Publisher | Elsevier |

Keywords | Rectangular graphene nanoribbons; Singlet-triplet excitation energies; Density functional methods; Theoretical benchmarking |

Link | http://dx.doi.org/10.1016/j.comptc.2011.09.021 |

Abstract |
Singlet-triplet (S0âT1) well-to-well (WWES-T) and vertical (VES-T) excitation energies of the [4Ãn] rectangular graphene nanoribbon series (n=2-6) were estimated using various semiempirical, Hartree-Fock (HF), density functional (DFT), and second order Moller-Plesset perturbation theory methods with the assumption of a closed-shell singlet state. Significant model chemistry dependent variability in theoretically obtained WWES-T/VES-T is evident for the rectangular graphene nanoribbons. With the exception of the B2PLYP density functional (which, along with the mPW2PLYP functional, combines exact HF exchange with an MP2-like correlation to the DFT calculation), all DFT, semiempirical, and HF methods investigated predict the onset of a negative WWES-T/VES-T (ground state triplet) starting somewhere between the [4Ã3] through [4Ã6] derivatives, with most functionals predicting a transition from a singlet to triplet ground state between the [4Ã4] and [4Ã5] rectangular graphene nanoribbons. Consistent with previous work on the n-acene series, MP2 WWES-T/VES-T estimates have a significant positive systematic bias and HF estimates have substantial negative systematic biases. Extrapolation of the B2PLYP results, which are in excellent agreement with prior FPA-QZ VES-T estimates, for any [mÃn] rectangular graphene nanoribbon derivatives predicts a vanishingly small singlet-triplet gap at the polymeric limit (mââ and/or nââ). |

Back to page 7 of list