The correlation coefficients of the fitting equations are all found to be of R 2 > 0.999, indicating the surprisingly satisfactory fitting quality. It is worth mentioning that our previous study on the optical nonlinearities of cyclo[2N]carbon (N = 3-15) shows that the size dependence of (hyper)polarizability follows different rules according to the parity of N in cyclic carbon molecules , while the change characteristics of carbon chains H-(C≡C) n -H (n = 3-9, 15) with odd and even C-C units are consistent.