Polishing the Gold Standard: The Role of Orbital Choice in CCSD(T) Vibrational Frequency Prediction
Polishing the Gold Standard: The Role of Orbital Choice in CCSD(T) Vibrational Frequency Prediction
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DOI：
10.1021/acs.jctc.0c00746
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发表时间：
2021-01-06
影响因子：
5.5
通讯作者：
Head-Gordon, Martin
中科院分区：
文献类型：
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作者：
Bertels, Luke W.;Lee, Joonho;Head-Gordon, Martin
虽然具有自旋限制的Hartree-Fock（RHF）轨道的CCSD（T）长期以来因其准确描述闭壳层相互作用的能力而受到称赞，但CCSD（T）对开壳层物质的性能更加不稳定，特别是当使用自旋不受限制的HF（UHF）参考时。以前的研究表明，当使用非HF分子轨道集（如Brueckner或Kohn-Sham密度泛函理论（DFT）轨道）作为参考时，开壳层系统的处理得到了改善。受正则化轨道优化的二阶Moller-Plesset微扰理论的成功启发（kappa-OOMP 2）轨道作为MP3的参考轨道，我们研究了用kappa-OOMP 2轨道和各种DFT轨道作为参考轨道，用CCSD（T）计算了一组36个闭壳层的修正基态谐振频率（29个中性粒子，6个阳离子，1个阴离子）和59个开壳层双原子物种（38个中性粒子，15个阳离子，6个阴离子）。所有计算均使用aug-cc-CVTZ基组。在这种情况下，使用kappa-OOMP 2轨道简化了观察到的UHF轨道和OOMP 2轨道的困难情况。删除两个多参考系统和12个系统与模糊的实验数据留下一个修剪的数据集。经过修剪的数据集的总体性能突出显示了CCSD（T）与B 97轨道参考（CCSD（T）：B 97）、CCSD（T）与kappa-OOMP 2轨道参考（CCSD（T）：kappa-OOMP 2）和CCSD（T）与B 97 M-rV轨道参考（CCSD（T）：B 97 M-rV），均方根值分别为8.48 cm（-1）、8.50 cm（-1）和8.75 cm（-1），优于CCSD（T）：UHF近5倍。此外，在闭壳和开壳子集上的性能表明，这些方法能够以相当的精度和鲁棒性处理开壳和闭壳系统。RHF轨道的CCSD（T）被认为对闭壳层物种的UHF有所改善，而在一些受限制的开壳层HF（ROHF）参考中的空间对称性破缺导致CCSD（T）与ROHF参考轨道的所有方法对开壳层物种的统计性能最差。kappa-OOMP 2轨道的使用也被证明在诊断可能妨碍CCSD（T）可靠性的多参考特征方面是有用的。
While CCSD(T) with spin-restricted Hartree-Fock (RHF) orbitals has long been lauded for its ability to accurately describe closed-shell interactions, the performance of CCSD(T) on open-shell species is much more erratic, especially when using a spin-unrestricted HF (UHF) reference. Previous studies have shown improved treatment of open-shell systems when a non-HF set of molecular orbitals, like Brueckner or Kohn-Sham density functional theory (DFT) orbitals, is used as a reference. Inspired by the success of regularized orbital-optimized second-order Moller-Plesset perturbation theory (kappa-OOMP2) orbitals as reference orbitals for MP3, we investigate the use of kappa-OOMP2 orbitals and various DFT orbitals as reference orbitals for CCSD(T) calculations of the corrected ground-state harmonic vibrational frequencies of a set of 36 closed-shell (29 neutrals, 6 cations, 1 anion) and 59 open-shell diatomic species (38 neutrals, 15 cations, 6 anions). The aug-cc-pwCVTZ basis set is used for all calculations. The use of kappa-OOMP2 orbitals in this context alleviates difficult cases observed for both UHF orbitals and OOMP2 orbitals. Removing two multireference systems and 12 systems with ambiguous experimental data leaves a pruned data set. Overall performance on the pruned data set highlights CCSD(T) with a B97 orbital reference (CCSD(T):B97), CCSD(T) with a kappa-OOMP2 orbital reference (CCSD(T): kappa-OOMP2), and CCSD(T) with a B97M-rV orbital reference (CCSD(T):B97M-rV) with RMSDs of 8.48 cm(-1), and 8.50 cm(-1), and 8.75 cm(-1) respectively, outperforming CCSD(T):UHF by nearly a factor of 5. Moreover, the performance on the closed- and open-shell subsets shows these methods are able to treat open-shell and closed-shell systems with comparable accuracy and robustness. CCSD(T) with RHF orbitals is seen to improve upon UHF for the closed-shell species, while spatial symmetry breaking in a number of restricted open-shell HF (ROHF) references leads CCSD(T) with ROHF reference orbitals to exhibit the poorest statistical performance of all methods surveyed for open-shell species. The use of kappa-OOMP2 orbitals has also proven useful in diagnosing multireference character that can hinder the reliability of CCSD(T).