【摘要】 本文从“离子基团理论”出发,并考虑A位离子晶格电场对（B₃O₆）^3-环的影响,采用CNDO/S近似计算了（B₃O₆）^3-基团的分子轨道,进而求得低温相偏硼酸钡（β-BaB₂O₄）晶体的倍频系数。计算结果与实验值符合,由此进一步证实了这一论点:β-BaB₂O₄晶体的倍频系数主要来自（B₃O₆）^3-基团中共轭π轨道的贡献。计算结果还表明,CNDO/S型近似是一种计算晶体中共价键基团分子轨道的有效方法。更多还原

【Abstract】 β-BaB2O4 crystal is a new-type ultraviolet SHG crystal as found in our Institute for the first time. In this paper, on the basis of our theoretical work of "An anionic group theory of non-linear optical effects of the crystals" and the theory of odd-ordered crystal field produced by A-site cation, we have calculated SHG coefficients of β-BaB2O4 crystal by using CNDO/S approximations. The calculated values agree satisfactorily with the experimental data, for both absolute values and relative sign of the above coefficients. The result shows that the conjugate π orbitals of anionic group （B3O6）3-give major contribution to the SHG coefficients. Moreover, it also shows that the CNDO/S-approximation is a suitable method for calculating molecular orbitals of cova-lent-bonded （B3O₆）3- group in crystals.更多还原