Spin polarization and third-order nonlinear optical properties of open-shell singlet graphene nanoflakes

Spin polarization and third-order nonlinear optical properties, second hyperpoalrizabilities (γ), of open-shell singlet graphene nanoflakes (GNFs) with hexagonal, rhombic and bow-tie shapes are investigated using a hybrid density functional theory method. The spatial spin polarization exhibits a strong structural dependence, i.e., edge shape effect, and the diradical character is also found to depend on the structure of zigzag-edged nanoflakes. These structural dependences of diradical characters of graphene nanoflakes are expected to provide a novel control scheme of the γ values.