Effect of cage size on the third-order optical properties of endohedral metallofullerenes Sc _3N@C _(2n) (2n = 68, 70, 78, and 80): A theoretical study

摘要

Geometrical structures of the investigated endohedral metallofullerenes Sc _3N@C _(2n) (2n = 68, 70, 78, and 80) were optimized at the B3LYP/6-31G* level. The analyses of electronic structures display that the contribution of fullerene cage to the lowest unoccupied molecular orbital decreases as the cage size increases. Based on the optimized structures, the time-dependent density functional theory combined with the sum-over-states method was used to investigate their nonlinear optical properties. Calculated third-order polarizabilities γ and two-photon absorption (TPA) cross-section δ do not present the monotone variation with the size of fullerene cage, with largest γ of 0.48 × 10 ~(-34) esu for Sc _3N@C _(78) in static state, and largest δ of 12.374 GM for Sc _3N@C _(70) in the wavelength of 902.5 nm. However, the obtained TPA resonant peaks shift red with the size of fullerene cage. By analyzing the electronic origin of the third-order optical properties, it is found that the charge transfers from the fullerene cage to the encapsulated Sc _3N cluster make important contributions to the studied properties.