However, since it is much more convenient to obtain the electron density of an isolated system through quantum chemistry calculations and that of a periodic system which consists of two cyclohexanes connected by an acetylene bridge in a biaxial conformation. It has been pointed out that this conformation is notably stabilized by intramolecular dispersion interaction, making its electronic energy lower than that of other conformations. Indeed, the NCI map clearly shows an evident green isosurface between the two cyclohexanes, reflecting the dispersion stabilization effect. Note that dispersion term corresponds to the attractive component of vdW interaction, while exchange-repulsion term corresponds to the repulsive component. Gonzá lez-Veloso et al. made full use of the NCI method to reveal noncovalent interactions in their study of the interaction between alkali metal ions and buckybowls, which serves as an interesting application example (see Fig. ). It is noteworthy that the sign(2) coloring method used in Fig. is the most commonly employed in the literature; however, some papers, such as Ref. , use different color scale ranges for better image clarity or due to conventions. Therefore, the color bar should always be clearly provided in an NCI map. Additionally, Fig. employs an RDG value of 0.55 to define the isosurfaces, which slightly differs from the RDG value used in Fig. . Fig. (a) shows the NCI map of complexes formed by different alkali metal cations and buckybowls. It can be seen that as the ionic radius increases from Li + to Cs + , the area of their interaction with buckybowl P1 also increases significantly. However, as indicated by the complexation energy in parentheses, the interaction strength between the ions and P1 decreases from Li + to Cs + , which is vividly reflected in the color of the isosurface changing from blue (relatively strong interaction) to green (very weak interaction). The underlying reason is that the polarization ability of alkali metal ions weakens progressively from Li + to Cs + . Fig.