TDDFT diagnostic testing and functional assessment for triazene chromophores

Peach, Michael J. G.; Le Sueur, C. Ruth; Ruud, Kenneth; Guillaume, Maxime; Tozer, David J.

Abstract

A simple diagnostic test based on orbital overlap [M. J. G. Peach et al., J. Chem. Phys., 2008, 128, 044118] may be used to help judge the reliability of excitation energies in time-dependent density functional theory (TDDFT) when using generalized gradient approximation (GGA) and hybrid functionals. Orbital plots are used to illustrate the test for a model tripeptide and for 4-(N,N-dimethylamino)benzonitrile, which are representative of systems containing low- and high-overlap charge-transfer excitations. The scheme is then applied to a series of triazene chromophores in solvent, highlighting the relationship between overlap and oscillator strength and its implications for theoretical absorption spectra. No low-overlap excitations are observed with a hybrid functional; a single one is identified using a GGA. To assess the diagnostic test and to judge functional performance, gas phase triazene TDDFT excitations are compared with correlated ab initio values. The diagnostic test correctly identifies two low-overlap problematic GGA excitations. However, it does not identify another problematic excitation where the electron is excited to a spatially extended orbital, which necessarily has reasonable overlap with the occupied orbital; an improved diagnostic quantity is required for such cases. The best agreement between TDDFT and correlated ab initio excitations is obtained using a Coulomb-attenuated functional; the errors are significantly smaller than from the GGA and hybrid functionals. The study provides further support for the high quality excitations from Coulomb-attenuated functionals, negating the need for diagnostic tests.

Citation

Peach, M. J. G., Le Sueur, C. R., Ruud, K., Guillaume, M., & Tozer, D. J. (2009). TDDFT diagnostic testing and functional assessment for triazene chromophores. Physical Chemistry Chemical Physics, 11(22), 4465-4470. https://doi.org/10.1039/b822941d

• Journal Article Type: Article
• Acceptance Date: Feb 6, 2009
• Online Publication Date: Mar 3, 2009
• Publication Date: 2009
• Deposit Date: Nov 26, 2024
• Journal: Physical Chemistry Chemical Physics
• Print ISSN: 1463-9076
• Electronic ISSN: 1463-9084
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 11
• Issue: 22
• Pages: 4465-4470
• DOI: https://doi.org/10.1039/b822941d
• Public URL: https://durham-repository.worktribe.com/output/3107205