Spectroscopic properties such as equilibrium distances, vibrational constants, rotational constants, dissociation energies, and excitation energies are calculated for nine heteronuclear diatomic molecules (PH, NF, NH, NO, CS, AlF, ClF, BeO and CF) using an interactive pair model (PNOF7s), that has been generalized for spin multiplet states, and its second order perturbation variant, NOF-MP2, which was also generalized for multiplets. The results obtained are compared with Complete Active Space (CASSCF) and Complete Active Space Perturbation Theory (CASPT2). It is shown that the potential energy curves provided by the PNOF functional for open shell diatomic molecules are in acceptable agreement with those from CASSCF and CASPT2. The spectroscopic constants depending at most on the second derivative of the potential energy are in good agreement with experiment, while those requiring the evaluation of the third and fourth derivatives show larger deviations from experiment and from those predicted by CASPT2. Thus, it is shown that the PNOF functional extension to multiplets is an alternative approach in predicting spectroscopic constants of molecules where static correlation plays an important role, like the open shell heteronuclear diatomic molecules studied in this work.

中文翻译：

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使用Piris自然轨道功能的开壳双原子分子的光谱性质

使用交互式对模型计算九个异核双原子分子（PH，NF，NH，NO，CS，AlF，ClF，BeO和CF）的光谱性质，例如平衡距离，振动常数，旋转常数，解离能和激发能（PNOF7s），已针对自旋多重态进行了概括，其二阶摄动变量NOF-MP2也针对多重态进行了概括。将获得的结果与完全活动空间（CASSCF）和完全活动空间摄动理论（CASPT2）进行比较。结果表明，由PNOF函数提供的用于开壳双原子分子的势能曲线与CASSCF和CASPT2的势能曲线可以接受。最多取决于势能的二阶导数的光谱常数与实验非常吻合，而需要评估三阶和四阶导数的光谱常数则显示出与实验以及与CASPT2预测的偏差更大。因此，显示出PNOF功能扩展至多重峰是预测分子的光谱常数的替代方法，其中静态相关性起着重要作用，例如在这项工作中研究的开壳异核双原子分子。