Although ionic bonds cannot be directly displayed by ELF, they can be visualized using the methods introduced in Section 2, such as IRI, IGMH, and NCI. Reprinted with permission from Ref. . Copyright 2018 American Chemical Society. (c) cyclo [18]carbon under external electric field of strength of 0.029 a.u. Reprinted with permission from Ref. . Copyright 2021 John Wiley and Sons. (d) Potassium hydroxide.