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|Title: ||Focal Point Analysis of the Singlet-Triplet Energy Gap of Octacene and Larger Acenes|
|Authors: ||Hajgato, Balazs|
Deleuze, Michael S.
|Issue Date: ||2011|
|Citation: ||The journal of physical chemistry. A, 115, p. 9282-9293|
|Abstract: ||A benchmark theoretical study of the electronic ground state and of the vertical and adiabatic singlet-triplet (ST) excitation energies of n-acenes (C4n+2H2n+4) ranging from octacene (n = 8) to undecacene (n = 11) is presented. The T1 diagnostics of coupled cluster theory and further energy-based criteria demonstrate that all investigated systems exhibit predominantly a 1Ag singlet closed-shell electronic ground state. Singlet-triplet (S0-T1) energy gaps can therefore be very accurately determined by applying the principle of a focal point analysis (FPA) onto the results of a series of single-point and symmetry-restricted calculations employing correlation consistent cc-pVXZ basis sets (X = D, T, Q, 5) and single-reference methods [HF, MP2, MP3, MP4SDQ, CCSD, and CCSD(T)] of improving quality. According to our best estimates, which amount to a dual extrapolation of energy differences to the level of coupled cluster theory including single, double, and perturbative estimates of connected triple excitations [CCSD(T)] in the limit of an asymptotically complete basis set (cc-pV∞Z), the S0-T1 vertical (adiabatic) excitation energies of these compounds amount to 13.40 (8.21), 10.72 (6.05), 8.05 (3.67), and 7.10 (2.58) kcal/mol, respectively. In line with the absence of Peierls distortions (bond length alternations), extrapolations of results obtained at this level for benzene (n = 1) and all studied n-acenes so far (n = 2-11) indicate a vanishing S0-T1 energy gap, in the limit of an infinitely large polyacene, within an uncertainty of 1.5 kcal/mol (0.06 eV). Lacking experimental values for the S0-T1 energy gaps of n-acenes larger than hexacene, comparison is made with recent optical and
electrochemical determinations of the HOMO-LUMO band gap. Further issues such as scalar relativistic, core correlation, and diagonal Born-Oppenheimer corrections (DBOCs) are tentatively examined.|
|Notes: ||Reprint Address: Deleuze, MS (reprint author), Hasselt Univ, Res Grp Theoret Chem & Mol Modelling, Agoralaan Gebouw D, B-3590 Diepenbeek, Belgium - Addresses: 1. Hasselt Univ, Res Grp Theoret Chem & Mol Modelling, B-3590 Diepenbeek, Belgium - E-mail Address: firstname.lastname@example.org|
|ISI #: ||000294076500023|
|Type: ||Journal Contribution|
|Validation: ||ecoom, 2012|
|Appears in Collections: ||Center of Molecular and Materials Modelling|
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