Theoretical study on the nonlinear optical properties of MX-chain

Summary form only given. By applying a two-band model and a perturbation approach, we investigate the various nonlinear optical properties of the halogen-bridged mixed-valence transition-metal complexes, PtC1, PtBr, and PtI. The theoretical third-harmonic generation (THG) spectra show two prominent peaks. For PtC1, one peak is near 0.8 eV and another, more intense, 1.6 eV. Both peaks are due to three-photon resonances. The 1.6 eV broad peak agrees very well with experimental data. The theoretically simulated electro-absorption spectra are also in full agreement with several experiments.