title: Origin of the Enhancement of the Second Hyperpolarizabilities of Metal-Carbon Bonds.
abstract: The spin-unrestricted coupled-cluster method was employed to investigate the origin of the second hyperpolarizabilities (γ) in model systems involving metal-carbon bonds with various bond lengths as a function of their diradical character (y) and charge transfer (CT). These systems exhibit unique features: (i) σ electrons give the dominant contribution to γ, (ii) the π electrons contribution to γ is negative, (iii) when the bond length increases, γ exhibits two positive extrema, which are associated with the CT nature and the intermediate diradical character, respectively, (iv) and one negative extremum corresponding to intermediate CT and diradical character, and (v) in the bond stretching process, the maximum γ amplitude per σ bond is about 7 times larger than that per π bond. These features are significantly different from those observed in pure organic systems.
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Shota
authors.initials: S
authors.lastname: Takamuku
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Kitagawa
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Nagami
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Jun-Ya
authors.initials: JY
authors.lastname: Fujiyoshi
authors.affiliation: Laboratoire de Chimie Théorique, University of Namur , rue de Bruxelles, 61, B-5000 Namur, Belgium.
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Nakano