Spectrum of Third Harmonic Generation of MX Complex

The theory of third harmonic generation of MX complex is presented on the basis of charge density wave model. The recently observed spectrum x⁽³⁾ ( ω ) of Pt-Cl complex can be well interpreted by this theory, which shows that the experimental peak at 1.8eV is produced by the two-photon resonance between the bottom of valence band and the top of conduction band. Besides, our theory predicts that there exist another peak below the observed region.