The axial tensorial components of the (hyper)polarizability of C 18 -(CO) n (n = 2, 4, and 6) obtained by the FF method are listed in Table . An intuitive comparison of them with the values derived analytically by CPKS method in Tables and is drawn in Fig. . It can be seen that there is almost no distinction in the calculated values of (hyper)polarizabilities between the two methods. Therefore, the reliability of the (hyper)polarizability density analysis and the decomposition of (hyper)polarizabilities to fragment contributions based on the FF method is fully guaranteed. The (hyper)polarizability density exhibits local contributions of different spatial regions to (hyper)polarizability, which is helpful in understanding the physical essence of molecular response properties in two axes except the direction with their largest tensorial component in static electric field were also studied, see Figs. and, respectively, for comparison. It can be observed that the (hyper)polarizability density isosurfaces of these two tensorial components are obviously narrow, especially for the first and second hyperpolarizabilities. And even more, under the same isovalue, the isosurfaces of Z-tensorial component are not even visible at all. A good correspondence is found between the isosurface features and the response values on these two axes, as in the case of the major tensorial components of (hyper)polarizability discussed above.