Cluster modeling of electronic structure and nonlinear properties for the optical materials MB6O10 (M= Cs-2, Li-2, CsLi)

The clusters Cs2B6O10, Li2B6O10, and CsLiB6O10, consisting in crystalline s tates, are employed to model the electronic structures and nonlinear optica l properties of optical materials CBO(CsB3O5), LBO(LiB3O5), and CLBO (CsLiB 6O10). The electronic structures and dynamic second-order polarizabilities of these clusters have been calculated using the intermediate neglect of di fferent overlap with singlet excited configuration-interaction method and i n combination with the sum-over-states method, respectively. Then, the seco nd-order susceptibilities of these three bulks have been estimated in terms of the microspecies number density and local-field correction factor at a low-frequency zone of photons. It is found that the top levels of the valen ce band derive from O 2p orbitals and the lowest edge of the conduction ban d derives from B 2p and O 2p orbitals. The calculated energy gap increases in the order of CsLiB6O10 (6.31 eV) <Cs2B6O10(6.66eV)<Li2B6O10 (7.26 eV), a s compared to the observed optical gap of crystals, CLBO (180 nm)<CBO (170 nm)<LBO (160 nm), individually. The calculated results show that the excite d-state charge transfers from O 2p to B value orbitals make the most signif icant contributions to the second-order susceptibility for all of these thr ee crystals. It is also found that the natures of orbitals both at the uppe r valence band and at the lowest edge of the conduction band are the least changed among the three clusters M(B6O10) (M = Cs-2, Li-2, CsLi), and that the high ionicity of cation and anionic group interaction results in a larg e NLO coefficient. Both the ionicity and the calculated nonlinear optical c oefficients decrease in the order of CBO>CLBO>LBO. This result will give a clue in designing a new nonlinear optical material with the same anionic gr oup. [S0163-1829(99)04339-8].