where Fj is the stepsize of an external electric field parallel to the principal axis and was set to be 0.003 a.u., which has been repeatedly confirmed to be very suitable for FF calculation . Herein, two wavelengths commonly used in experiments (λ = 1907 and 1064 nm) were applied in the calculations of this work to compare the dispersion effect on the first hyperpolarizability of the C18 derivative molecules designed.