Fig. 1. Electronic elliptic orbit of an atom in bound state and its equivalent charge-distributions in space

Fig. 2. Schematic of collision cross section of jumping electron from i to j energy level

Fig. 3. Numerical simulation of PSPI based on QILO^[25]. (a) PSPI structure; (b) linear absorption spectrum; (c) fitting of QILO model to spectrum; (d) fitting of two-photon absorption cross section of PSPI molecule based on QILO model

Fig. 4. Sketch map of the actual collision between the jumping electron and the environment atom in the crystal

Fig. 5. Numerical simulation of Li₂SnTeO₆ crystal based on QILO. (a) Crystal structure; (b) linear absorption spectrum; (c) fitting of QILO model to spectrum; (d) second-order electric susceptibility of crystal calculated based on QILO model (assuming no other absorption peak in the wavelength range of 200‒1100 nm)

Fig. 6. Numerical simulation of CsClO₃ crystal based on QILO. (a) Crystal structure; (b) linear absorption spectrum; (c) fitting of QILO model to spectrum; (d) second-order electric susceptibility of crystal calculated based on QILO model (assuming no other absorption peak in the wavelength range of 200‒1100 nm)

Fig. 7. Numerical simulation of Na₂Nb₄O₁₁ crystal based on QILO. (a) Crystal structure^[27]; (b) linear absorption spectrum; (c) fitting of QILO model to spectrum; (d) second-order electric susceptibility of crystal calculated based on QILO model (assuming no other absorption peak in the wavelength range of 200‒1100 nm)