Singlet L-a and L-b Bands for N-Acenes (N=2-7): A CASSCF/CASPT2 Study

Author(s)

Bettanin, Fernanda ; Ferrao, Luiz F. A. ; Pinheiro, Jr., Max ; Aquino, Adelia J. A. ; Lischka, Hans ; Machado, Francisco B. C. ; Nachtigallova, Dana

• Document type: Journal article
• Source: JOURNAL OF CHEMICAL THEORY AND COMPUTATION; v. 13, n. 9, p. 4297-4306, SEP 2017.
• Web of Science Citations: 9

Abstract

In this work CASPT2 calculations of polyacenes (from naphthalene to heptacene) were performed to find a methodology suitable for calculations of the absorption spectra, in particular of the La (B-2u state) and L-b (B-3u state) bands, of more extended systems. The effect of the extension of the active space and of freezing a orbitals was investigated. The MCSCF excitation energy of the B-2u state is not sensitive to the size of the active space used. However, the CASPT2 results depend strongly on the amount of a orbitals frozen reflecting the ionic character of the B-2u state. On the other hand, the excitation energies of the B-3u state are much more sensitive to the size of the active space used in the calculations reflecting its multiconfigurational character. We found a good agreement with experimental data for both bands by including 14 electrons in 14 pi orbitals in the active space followed by the CASPT2(14,14) perturbation scheme in which both sigma and pi orbitals are included. (AU)

• FAPESP's process: 15/50018-9 - High-level quantum chemical investigations of defect structures in model graphene systems
• Grantee: Francisco Bolivar Correto Machado
• Support Opportunities: Regular Research Grants
• FAPESP's process: 14/24155-6 - Study of electronic states in polycyclic aromatic hydrocarbons and their properties as models of electronic graphene structures
• Grantee: Francisco Bolivar Correto Machado
• Support Opportunities: Regular Research Grants