title: Long-range corrected density functional theory study on static second hyperpolarizabilities of singlet diradical systems.
abstract: Within the spin-unrestricted density functional theory (DFT) the long-range correction (LC) scheme combined with the Becke-Lee-Yang-Parr exchange-correlation functional, referred to as LC-UBLYP method, has been applied to the calculation of the second hyperpolarizability (gamma) of open-shell singlet diradical systems of increasing complexity and has demonstrated good performance: (i) for the simplest H(2) dissociation model, the gamma values calculated by the LC-UBLYP method significantly overshoot the full configuration interaction result but reproduce qualitatively the evolution of gamma as a function of the diradical character, (ii) for small singlet diradical 1,3-dipole systems, the diradical character dependence of gamma determined by the UCCSD and UCCSD(T) reference methods is reproduced semiquantitatively by the LC-UBLYP method except in the small diradical character region, where the spin-unrestricted solutions coincide with spin-restricted solutions, (iii) the LC-UBLYP method also closely reproduces the UCCSD(T) results on the diradical character dependence of gamma of the p-quinodimethane model system, particularly in the intermediate and large diradical character regions, whereas it shows an abrupt change for a diradical character (y) close to 0.2 originating from the triplet instability, (iv) the reliability of LC-UBLYP to reproduce reference coupled cluster results on open-shell singlet systems with intermediate and large diradical characters has also been substantiated in the case of gamma of 1,4-bis-(imidazol-2-ylidene)-cyclohexa-2,5-diene (BI2Y), then (v), for real systems built from a pair of phenalenyl radicals separated by a conjugated linker, the LC-UBLYP results have been found to closely match the UBHandHLYP values-which, for small systems are in good agreement with those obtained using correlated molecular orbital methods-whereas the UB3LYP results can be much different. These results are not only important from the viewpoint of an efficient determination of the nonlinear optical properties of open-shell singlet systems, but also from the viewpoint of defining new challenges for elaborating improved exchange-correlation functionals.
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. rkishi@cheng.es.osaka-u.ac.jp
authors.forename: Ryohei
authors.initials: R
authors.lastname: Kishi
authors.forename: Sean
authors.initials: S
authors.lastname: Bonness
authors.forename: Kyohei
authors.initials: K
authors.lastname: Yoneda
authors.forename: Hideaki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Nakano
authors.forename: Edith
authors.initials: E
authors.lastname: Botek
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne
authors.forename: Takashi
authors.initials: T
authors.lastname: Kubo
authors.forename: Kenji
authors.initials: K
authors.lastname: Kamada
authors.forename: Koji
authors.initials: K
authors.lastname: Ohta
authors.forename: Takao
authors.initials: T
authors.lastname: Tsuneda