7Li2分子2 3Σ+g激发态的解析势能函数、谐振频率及振动能级

使用Gaussian03程序包中的“对称性匹配簇/对称性匹配簇-组态相互作用”方法, 利用多个基组对⁷Li₂分子2³Σ⁺_g态的平衡几何进行了优化计算. 同时, 在优化得到的平衡位置附近、于同一条件下通过精细的单点能扫描, 获得了相应基组下的平衡核间距. 发现两者的结果不一致，对不一致的原因进行了解释. 分析表明，由单点能扫描得到的平衡核间距应更为合理. 同时也得出了6-311++G(3df,3pd)，6-311++G(2df,2pd) 及6-311++G(2df,pd)基组均为较优基组的结论.于2.5a₀—37a₀的范围内利用6-311++G(3df,3pd)基组进行单点能扫描并使用最小二乘法拟合出了该态的解析势能函数. 利用解析势能函数的物理意义并结合Rydberg-Klein-Rees方法, 计算出了其相应的谐振频率, 进而计算了其他光谱常数. 为便于比较和分析, 对基态也进行了相应的计算.利用得到的解析势能函数, 对2³Σ⁺_g态的振动能级及振动经典转折点也进行了计算. 关键词： 势能函数 谐振频率 振动能级 Murrell-Sorbie函数

Investigation of analytic potential energy function, harmonic frequency and vibrational levels for the 23Σ+g state of spin-aligned dimer 7Li2

Using the symmetry adapted cluster/symmetry adapted cluster-configuration interaction(SAC/SAC-CI) method in Gaussian03 program package, the equilibrium geometry of the 2³Σ⁺_g state of spin-aligned dimer ⁷Li₂ is calculated at a number of basis sets. At the same time, the single-point energy scanning calculation is also made at each basis set near the equilibrium internuclear separation obtained by the geometry optimization so as to attain the more accurate result. A disagreement between the result obtained by the geometry optimization and that obtained by the single-point energy scanning calculation is found. Our analysis shows that the result obtained by the single-point energy scanning calculation should be more reasonable. We drew the conclusion that the basis sets 6-311++G(3df,3pd), 6-311++G(2df,2pd) and 6-311++G(2df,pd) are the most suitable ones for the 2³Σ⁺_g state calculation. The complete potential energy curve is further scanned at SAC-CI/6-311++G(3df,3pd) level of theory for the state over the internuclear separation range from 2.5a₀ to 37a₀, then a least squares fit to the Murrell-Sorbie function is made, at last the harmonic frequency is calculated, which is in good agreement with other theoretical results. At the same time, the same calculations are made for the ground state for comparison. In addition, we have also calculated the vibrational levels and the classical turning points.