中文摘要：

The structures of barbituric acid derivatives substituted with Schiff base were optimized using ab initio HF method at 6-31G basis set. Based on the optimized structures, the electronic spectra were obtained by INDO/CI method. The second-order nonlinear optical (NLO) coefficients βμ were calculated according to the sum-over-states (SOS) formula. In addition, the effect of conjugation on electronic spectra and second-order NLO coefficients was investigated. The influence of exchange between C and N atoms as well as the substituted effect on the barbituric acid was discussed. It was indicated that the exchange between C and N atoms on Schiff base is important for enhancing the NLO coefficient of the whole molecule with donor and acceptor (D-A). Meanwhile significant changes in electron donation and acception were observed as substituents changes positions. Among the designed models, molecule 1b has maximal βμ value of 124.65×10^-30 esu. About molecule lb, barbituric acid is considered as an accepted electronic group and the position of N atom on Schiff base is close to it.

英文摘要：

The structures of barbituric acid derivatives substituted with Schiff base were optimized using ab initio HF method at 6-31G basis set. Based on the optimized structures, the electronic spectra were obtained by INDO/CI method. The second-order nonlinear optical (NLO) coefficients βμ were calculated according to the sum-over-states (SOS) formula. In addition, the effect of conjugation on electronic specra and second-order NLO coefficients was investigated. The influence of exchange between C and N atoms as well as the substituted effect on the barbituric acid was discussed. It was indicated that the exchange between C and N atoms on Schiff base is important for enhancing the NLO coefficient of the whole molecule with donor and acceptor (D-A). Meanwhile significant changes in electron donation and acception were observed as substituents changes positions. Among the designed models, molecule lb has maximal βμ value of 124.65×10?-30 esu. About molecule lb, barbituric acid is considered as an accepted electronic group and the position of N atom on Schiff base is close to it.