Size and hydrogen saturation effects on third-order polarizabilities of Si clusters

► Third-order polarizability of hydrogenated silicon clusters up to 18Å diameter. ► TDDFT combined with SOS method. ► The sign of γ at low input photon energy changes from positive to negative when the ratio of hydrogen saturation increases. ► The magnitude of γ increases with a decrease in silicon cluster size. ► The solvent effect does not change the relative magnitude of γ for the Si-nc.