Publication: A comparison of density functional theory (DFT) methods for estimating the singlet-triplet (S0-T1) excitation energies of benzene and polyacenes
All || By Area || By Year| Title | A comparison of density functional theory (DFT) methods for estimating the singlet-triplet (S0-T1) excitation energies of benzene and polyacenes | Authors/Editors* | S Rayne, K Forest |
|---|---|
| Where published* | Computational and Theoretical Chemistry |
| How published* | Journal |
| Year* | 2011 |
| Volume | 976 |
| Number | |
| Pages | 105-112 |
| Publisher | Elsevier |
| Keywords | polyacenes; singlet-triplet excitation energies; density functional methods; benchmarking |
| Link | http://dx.doi.org/10.1016/j.comptc.2011.08.010 |
| Abstract |
Singlet-triplet (S0-T1) well-to-well (WWES-T) and adiabatic (AES-T) excitation energies of benzene and the linear polyacenes naphthalene through decacene were estimated using a range of density functional theory (DFT) methods and basis sets along with the assumption of a closed-shell singlet state. Via single exponential decay regression based extrapolations to the polymeric limit, significant variability in theoretically obtained WWES-T /AES-T predicted for longer polyacenes is evident that is primarily dependent on the model chemistry employed, with minor variations due to basis set incompleteness and zero-point energy (ZPE) corrections. With the exception of the B2PLYPD density functional (which, along with the mPW2PLYPD functional, combines exact HF exchange with an MP2-like correlation to the DFT calculation), all DFT methods investigated predict a negative WWES-T /AES-T (ground state triplet) at the polymer limit, with most functionals predicting a transition from a singlet to triplet ground state between octacene and decacene. Extrapolation of the B2PLYPD results predicts a vanishingly small singlet-triplet gap at the polymeric limit for an infinitely long homolog. Hartree-Fock calculations significantly underestimate the polyacene WWES-T /AES-T, whereas MPn methods overestimate the singlet-triplet gap but display a convergence toward experimental values with increasing truncation order and substitutions. The B2PLYPD and mPW2PLYPD functionals appear to balance the WWES-T /AES-T underestimating tendency of HF/DFT methods for longer polyacenes against the propensity for MPn methods to overestimate the WWES-T /AES-T for these compounds, and predict all acenes from benzene through decacene will be ground state singlets with positive singlet-triplet gaps. |
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