7LiH分子基态及若干激发态的平衡几何及垂直激发能的从头算

摘要

使用"对称性匹配簇-组态相互作用方法"(SAC/SAC-CI),在多种基组下计算了7LiH分子X1Σ+、A1Σ+、B1Π及b3Π态的平衡几何,并将由"几何优化"得到的相应各态的平衡几何与"单点能扫描"得到的结果进行了比较.比较的结果表明,由"几何优化"得到的相应各态的平衡几何,与"单点能扫描"得到的结果存在着差异.分析的结果表明,在完全活性空间中,由"SAC/SAC-CI"方法进行"单点能扫描"得到的结果,比"几何优化"得到的结果更加合理.首次报告了使用6-311G(3df,3pd)基组进行"单点等扫描"得到的相应各态的平衡几何.其值分别是:基态(X1Σ+)为0.1588 nm、单重态的第一激发态(A1Σ+)为0.2487 nm、单重态的第二激发态(B1Π)为0.2434 nm、三重态的第二激发态(b3Π)为0.1958 nm.这一计算结果与实验值非常接近.还研究了从基态到上述相应各态的垂直激发能,在基态的平衡位置处,其值分别为(A1Σ+←X1Σ+)3.613 eV、(B1Π←X1Σ+)4.612 eV和(b3Π←X1Σ+)4.233 eV.与其它理论计算结果进行比较后得出,本文的计算结果非常接近于使用很复杂的计算方法获得的结果.%The comparison between single-point energy scanning(SPES)and geometry optimization(OPT)in determining the equilibrium geometry of 7LiH molecule is made at numerous basis sets using a symmetry-adapted-cluster/symmetry-adapted-cluster configuration-interaction(SAC/SAC-CI)method.The difference of the results obtained by SPES and by OPT is reported.The conclusion is gained that the results obtained by SPES are more reasonable than those obtained by OPT in the SAC/SAC-CI calculations in full active space.The accurate equilibrium geometries of the X1Σ+,A1Σ+,B1Π and b3Π states are firstly calculated using the SAC/SAC-CI method at 6-311G(3df,3pd)basis set,and are of 0.1588 nm for the X1Σ+ state,0.2487 nm for the A1Σ+ state,0.2434nm for the B1Π state and 0.1958nm for the b3Π state,respectively.The vertical excitation energies from the ground to A1Σ+,B1Π and b3Π states are calculated,and are of 3.613 eV for the A1Σ+ state,4.612 eV for the B1Π state and 4.233 eV for the b3Π state at the ground-state equilibrium separation,respectively.Comparison of the theoretical calculations of equilibrium internuclear separations for these states with those obtained by previous theories clearly show that the present work is in excellent agreement with experimental data.And the vertical excitation energies from the ground to these excited states are much close to those attained by very complicated methods.