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首页> 外文期刊>The Journal of Chemical Physics >Comparative ab initio studies on the molecular structure and spectroscopic properties of FeF2: Single reference versus multireference methods
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Comparative ab initio studies on the molecular structure and spectroscopic properties of FeF2: Single reference versus multireference methods

机译：FeF2分子结构和光谱性质的从头开始比较研究：单参考法还是多参考法

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The electronic excitation energies, molecular geometry, quadratic force fields, and vibrational frequencies in the ground (5)Delta(g) and low-lying excited (5)Sigma(+)(g) and (5)Pi(g) electronic states of iron difluoride are studied at sophisticated levels of theory. Two families of basis sets, nonrelativistic and Douglas-Kroll-Hess relativistic, are used that range in quality from triple-zeta to quintuple-zeta. These are augmented by additional diffuse functions (on fluorine atoms) and tight functions (on all atoms) for the description of core-valence correlation and utilized to determine complete basis set molecular properties. The quality of electron correlation treatment using conventional single reference coupled cluster methods CCSD and CCSD(T) is compared to that attained at the multiconfigurational quasidegenerate second-order perturbation theory (CASSCF+MCQDPT2) and the electron attachment equation-of-motion coupled cluster (EOMEA-CCSD) levels. Spin-orbit coupling effects are studied by the SO-MCQDPT2 method using the full Breit-Pauli spin-orbit operator. Effects of spin contamination in the coupled cluster molecular calculations are carefully analyzed. Results of the single reference CCSD(T) and multireference calculations are found to be in a remarkable agreement. The calculations indicate that the EOMEA-CC approach provides a suitable tool for an accurate treatment of FeF2 and other systems where delicate electron correlation effects have to be carefully dealt with. The inclusion of relativistic effects is shown to be necessary for an accurate description of the molecular geometry and excitation energies of FeF2. The results of calculations are in good agreement with the experimental data available. The predicted FeF2 molecular properties are compared to those of the related FeF3. (C) 2008 American Institute of Physics.
机译：（5）Delta（g）和低洼激发的（5）Sigma（+）（g）和（5）Pi（g）电子态的电子激发能，分子几何结构，二次力场和振动频率在复杂的理论水平上研究了二氟化铁的含量。使用了两组相对论的基础集，即相对论论者和道格拉斯·克洛尔·赫斯相对论论者，其质量范围从三重Zeta到五重Zeta。为了描述核心价相关性，通过附加的扩散函数（在氟原子上）和紧密函数（在所有原子上）增强了这些值，并用于确定完整的基础分子性质。比较了使用传统的单参考耦合簇方法CCSD和CCSD（T）进行的电子相关处理的质量与在多构型准生成第二级微扰理论（CASSCF + MCQDPT2）和电子附着运动方程耦合簇所获得的质量（ EOMEA-CCSD）级别。使用完整的Breit-Pauli自旋轨道算子，通过SO-MCQDPT2方法研究了自旋轨道耦合效应。仔细分析了自旋污染对偶合簇分子计算的影响。发现单参考CCSD（T）和多参考计算的结果具有显着的一致性。计算表明，EOMEA-CC方法为准确处理FeF2和其他系统（其中必须仔细处理电子相关效应）提供了合适的工具。事实证明，包括相对论效应对于准确描述FeF2的分子几何结构和激发能是必要的。计算结果与可用的实验数据高度吻合。将预测的FeF2分子特性与相关的FeF3的分子特性进行比较。 （C）2008美国物理研究所。

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