Assessing long-range corrected functionals with physically-adjusted range-separated parameters for calculating the polarizability and the second hyperpolarizability of polydiacetylene and polybutatriene chains.

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.