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

► Approximate spin-projection scheme (ASP) with long-range corrected UDFT. ► Applicability of ASP-UBLYP to one-electron reduced density and (hyper)polarizability of diradical molecules. ► Analysis based on the (hyper)polarizability density. ► Diradical character dependences of (hyper)polarizability for diradical molecules.