Li_2分子X^1∑_g^+,A^1∑_u^+和B^1∏_u态的势能函数

Analytical potential energy functions for the electronic states X ~1∑_g^+ , A ~1∑_u^+ and B ~1∏_u of Li_2 molecule

使用SAC/SAC-CI方法,利用D95、D95(d)、6-311g以及6-311g(d)等基组,对Li2分子的基态(X1∑g+)、第一激发态(A1∑u+)及第二激发态(B1∏u)的平衡结构和谐振频率进行了优化计算。通过对四个基组的计算结果的比较,得出了D95(d)基组为四个基组中的最优基组的结论;使用D95(d)基组,利用SAC的GSUM(Group Sum of Operators)方法对基态(X1∑g+)、SAC-CI的GSUM方法对激发态(A1∑u+和B1∏u)进行单点能扫描计算,用正规方程组拟合Murrell-Sorbie函数,得到了相应电子态的完整势能函数;从得到的势能函数计算了与基态(X1∑g+)、第一激发态(A1∑u+)和第二激发态(B1∏u)相对应的光谱常数(Be,αe,ωe和ωexe),结果与实验数据较为一致。其中,基态、第一激发态与实验数据吻合得非常好。

The energies, equilibrium geometries and harmonic frequencies of the three electronic states (the ground state X 1∑g+ , the first state A 1∑u+ and the second state B 1∏u) of Li2 molecule have been calculated using the GSUM (Group Sum of Operators) method of SAC/ SAC - CI with the basis sets D95, D95(d), 6 -311g, and 6 - 311g(d). Comparing among the above-mentioned four basis sets, the conclusion is gained that the basis set D95(d) is the most suitable for the energy calculation of Li2 molecule. The whole potential curves for these three electronic states are further scanned using SAC/D95(d) method for the ground state and SAC-CI/D95(d) method for the excited states, then have a least square fitted to Murrell-Sorbie function, and last the spectroscopy constants (Be, αe, ωe, and ωexe ) are calculated, which are in good agreement with the experimental data. It is believed that Murrell-Sorbie function form and SAC/ SAC - CI method are suitable not only for the ground state, but for the low-lying excited states as well.