MgH分子X^2Σ^＋,A^2Π和B^2Σ^＋电子态的势能函数

Analytical potential energy function for the electronic states X^2Σ^+,A^2Π and B^2Σ^+ of MgH molecule

利用QCISD(T),SAC-CI方法和cc-pVQZ,aug-cc-pVTZ,6-311++G及6-311++G(3df,2pd)基组,对MgH分子的基态X2Σ+,第一简并激发态A2Π和第二激发态B2Σ+的结构进行优化计算.通过对4个基组计算结果进行比较,得出6-311++G(3df,2pd)基组为最优基组.使用6-311++G(3df,2pd)基组和QCISD(T)方法对基态X2Σ+,SAC-CI方法对激发态A2Π和B2Σ+进行单点能扫描计算,然后采用Murrell-Sorbie函数及修正的Murrell-Sorbie+C6函数进行拟合,得到了相应电子态的势能函数参数和对应的光谱常数.计算结果表明,用修正的Murrell-Sorbie+C6函数计算得到的MgH分子基态和第一简并激发态的光谱常数ωe,ωexe,Be,αe与实验数据吻合很好.表明修正后的Murrell-Sorbie+C6函数能更为准确地描述MgH分子的基态和第一激发态的势能函数.

The equilibrium geometries of three electronic states X^2Σ^＋, A^2Π and B^2Σ^＋ of MgH molecule have been calculated using the SAC-CI and QCISD （T） methods with the basis sets cc-pVQZ, aug-cc-pVTZ, 6-311 ＋ ＋ G and 6-311 ＋ ＋ G （3df, 2pd）. Comparing the above mentioned four basis sets,the conclusion is obtained that the basis set 6-311 ＋＋ G （3df, 2pd） is the most suitable for the energy calculation of MgH molecule. The whole potential curves for three electronic states are further scanned using QCISD （T）/6-311 ＋＋ G （3df,2pd） method for the ground state and SAC-CI/6-311 ＋＋ G （3df,2pd） method for the excited states. The potential energy functions and relevant spectrum constants ωe,ωexe,Be,αe of these states are obtained by fitting to the Murrell-Sorbie function and the modified Murrell-Sorbie ＋ C6 function, respectively. The results showed that the spectral constants derived from the modified Murrell-Sorbie ＋ C6 function are in very good agreement with the experimental data, and the modified Murrell-Sorbie ＋ C6 function can correctly describe the potential energy function of the ground state and the first degenerate state of MgH molecule.