title: Low-Lying ππ* States of Heteroaromatic Molecules: A Challenge for Excited State Methods.
abstract: The description of low-lying ππ* states of linear acenes by standard electronic structure methods is known to be challenging. Here, we broaden the framework of this problem by considering a set of fused heteroaromatic rings and demonstrate that standard electronic structure methods do not provide a balanced description of the two (typically) lowest singlet state (La and Lb) excitations. While the Lb state is highly sensitive to correlation effects, La suffers from the same drawbacks as charge transfer excitations. We show that the comparison between CIS/CIS(D) can serve as a diagnostic for detecting the two problematic excited states. Standard TD-DFT and even its spin-flip variant lead to inaccurate excitation energies and interstate gaps, with only a double hybrid functional performing somewhat better. The complication inherent to a balanced description of these states is so important that even CC2 and ADC(2) do not necessarily match the ADC(3) reference.
authors.affiliation: Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Antonio
authors.initials: A
authors.lastname: Prlj
authors.affiliation: Kimika Fakultatea, Euskal Herriko Unibersitatea & Donostia International Physics Center, Paseo Manuel de Lardiazabal, 4, 20018 Donostia, Spain.
authors.forename: María Eugenia
authors.initials: ME
authors.lastname: Sandoval-Salinas
authors.affiliation: Kimika Fakultatea, Euskal Herriko Unibersitatea & Donostia International Physics Center, Paseo Manuel de Lardiazabal, 4, 20018 Donostia, Spain.|IKERBASQUE - Basque Foundation for Science, 48013 Bilbao, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Casanova
authors.affiliation: Chimie Et Interdisciplinarité, Synthèse, Analyse, Modélisation (CEISAM), UMR CNRS 6320, BP 92208, Université de Nantes , 2, Rue de la Houssinière, 44322 Nantes Cedex 3, France.|Institut Universitaire de France (IUF), 1 rue Descartes, 75005 Paris Cedex 05, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Jacquemin
authors.affiliation: Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Clémence
authors.initials: C
authors.lastname: Corminboeuf