Tuned long-range corrected density functional theory method for evaluating the second hyperpolarizabilities of open-shell singlet metal-metal bonded systems

► The performance of the LC-UBLYP method for γ in metal-metal bonded systems. ► Significant dependence of γ on the range separating parameter (μ). ► The optimal μ lies between 0.7−0.9 bohr−1.