Methylammmonium lead iodide perovskites(CH_3NH_3PbI_3) have received wide attention due to their superior optoelectronic properties. We performed first-principles calculations to investigate the structural, electronic, and optical properties of mixed halide perovskites CH_3NH_3Pb(I_(1-y)X_y)_3(X = Cl, Br; y = 0, 0.33, 0.67). Our results reveal the reduction of the lattice constants and dielectric constants and enhancement of band gaps with increasing doping concentration of Cl-/Br-at I-. Electronic structure calculations indicate that the valance band maximum(VBM) is mainly governed by the halide p orbitals and Pb 6 s orbitals, Pb 6 p orbitals contribute the conduction band minimum(CBM) and doping does not change the direct semiconductor material. The organic cation [CH_3NH_3]^+does not take part in the formation of the band and only one electron donates to the considered materials. The increasing trends of the band gap with Cl content from y = 0(0.793 eV) to y = 0.33(0.953 eV) then to y = 0.67(1.126 eV). The optical absorption of the considered structures in the visible spectrum range is decreased but after doping the stability of the material is improving.
Metal complexes with excellent nonlinear optical(NLO) properties have attracted considerable attention. The geometry structure, electronic spectra and NLO properties of 2,2?-bidipyrrins(L) and mono-and bimetal Ir(I)/Rh(I)–L complexes have been investigated by density functional theory method. Our calculations revealed that L with planar configuration shows the largest first hyperpolarizability value, which is 2.2 to 5.5 times larger than that of others. It is attributed to the single direction of intramolecular charge transfer. When metal ions were embedded in ligands, the first hyperpolarizability values of mono-and bimetal Ir/Rh(I)–L complexes were smaller than that of L, and that of bimetal Ir/Rh(I)–L complexes were smaller than the corresponding monometallic Ir/Rh(I)–L. This is caused by the intramolecular charge transfer from multiple directions as well as the amount of charge transfer. On the other hand, on increasing the number of metal ions, the charge transfer in the opposite direction cancels each other more obviously. Our work would provide some theoretical reference for the second-order NLO responses of mono-and bimetal complexes.
