Approximate spin-projected spin-unrestricted density functional theory method: application to the diradical character dependences of the (hyper)polarizabilities in p-quinodimethane models

• Published in: Chemical physics letters Vol. 501; no. 1-3; pp. 140 - 145
• Main Authors: Nakano, Masayoshi, Minami, Takuya, Fukui, Hitoshi, Yoneda, Kyohei, Shigeta, Yasuteru, Kishi, Ryohei, Champagne, Benoît, Botek, Edith
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 06.12.2010
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/j.cplett.2010.10.057

The approximate spin projected spin-unrestricted density functional theory with long-range correction, ASP-LC-UBLYP, method with a range separating parameter μ = 0.47 is predicted to provide reliable one-electron properties such as the (hyper)polarizabilities of delocalized open-shell singlet molecules over a wide range of diradical characters. To demonstrate the performance of a novel approximate spin-projected (ASP) spin-unrestricted density functional theory (UDFT) method, we examine the diradical character dependences of the static polarizability (α) and second hyperpolarizability (γ) of a model open-shell singlet molecule, p-quinodimethane (PQM), using several hybrid and long-range corrected (LC) exchange-correlation functionals. The ASP-LC-UBLYP method with a range separating parameter μ = 0.47 is found to reproduce semi-quantitatively the diradical character dependences of α and γ of the PQM model calculated using the strongly-correlated UCCSD(T) method.