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Updated: May 2, 2026

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
Assessing long-range corrected functionals with physically-adjusted range-separated parameters for calculating the
Sébastien Nénon1, Benoît Champagne, Milena I Spassova
1Laboratoire de Chimie Théorique, Unité de Chimie Physique Théorique et Structurale, University of Namur, rue de Bruxelles, 61, B-5000 Namur, Belgium. sebastien.nenon@unamur.be benoit.champagne@unamur.be.
Abstract:
The use of physically-adjusted range-separated parameter (μ) together with long-range corrected exchange-correlation functionals is shown not to be reliable for calculating the polarizability (α) and the second hyperpolarizability (γ) of large π-conjugated systems. This statement has been substantiated by calculating the polarizability and the second hyperpolarizability of increasingly large polydiacetylene and polybutatriene chains in comparison with reference data evaluated at the coupled-cluster singles and doubles with perturbative estimation of the triples [CCSD(T)] level. Further comparisons highlight that long-range corrected exchange-correlation functionals with conventional and larger range-separated parameters perform better for α (μ = 0.47) and γ (μ = 0.33 and 0.47) but for polybutatriene chains none can describe satisfactorily the chain length evolution of γ. On the other hand, Møller-Plesset second- and fourth-order values are in closer agreement with CCSD(T), except for γ of polybutatriene, which is strongly overestimated.
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