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arXiv 2109.13380physics.chem-ph
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Coupled Cluster电子性质对参考行列式的敏感性:Kohn-Sham轨道能否比Hartree-Fock轨道更有利?

Sensitivity of Coupled Cluster Electronic Properties on the Reference Determinant: Can Kohn-Sham Orbitals Be More Beneficial than Hartree-Fock Orbitals?

Zsolt Benedek, Paula Tímár, Tibor Szilvási, Gergely Barcza

AI总结:

本研究比较HF-CC与KS-CC方法,发现KS-CC在相同计算成本下系统性地比HF-CC更偏离FCI极限,但在高CC水平下参考轨道影响可忽略,KS-CC可绕过HF收敛困难。

摘要:

Coupled cluster计算传统上基于Hartree-Fock参考轨道(HF-CC方法)进行。然而,文献中多次提出,在相同的计算成本下,使用Kohn-Sham参考(KS-CC方法)可能比HF-CC获得更好的性能。在本理论研究中,我们通过比较广泛应用的截断CC计算(CCSD、CCSD(T)、CCSDT)与全组态相互作用(FCI)极限的结果,重新审视了HF-CC和KS-CC方法的关系。与物理意义模糊的波函数诊断或具有相当不确定性的实验数据相比,FCI作为无可争议的精度参考点。我们发现,除了偶然的例外,与HF-CC相比,Kohn-Sham参考的CC方法表现出系统性的恶化,即在相同的coupled cluster水平下,KS-CC的分子性质(电子能量和密度)总是比HF-CC得到的性质更偏离FCI极限。此外,在CC计算中引入常见近似(冻结核、密度拟合)会导致KS参考情况下的误差显著更高。我们得出结论,使用KS参考轨道预计不会提高低水平CC能量学的可靠性。尽管如此,所研究化学反应各组分产生的分子误差可能幸运地相互抵消,从而产生比HF-CC更好的错觉。还值得注意的是,在足够高的CC水平下,参考轨道的选择对结果的影响可以忽略不计,这可以通过测试计算或双激发幅值的大小来估计。因此,应用KS-CC并非不合理,因为它可能绕过HF收敛的困难。

英文摘要:

Coupled cluster calculations are traditionally performed over Hartree-Fock reference orbitals (HF-CC methodology). However, it has been repeatedly argued in the literature that the use of a Kohn-Sham reference (KS-CC methodology) might result in improved performance relative to HF-CC at the same computational cost. In the present theoretical study, we re-examine the relation of HF-CC and KS-CC methods by comparing the results of widely applied truncated CC calculations (CCSD, CCSD(T), CCSDT) to the limit of full configuration interaction (FCI), which in contrast to wave-function diagnostics with vague physical meaning or experimental data with considerable uncertainty serves as an undebatable reference point of accuracy. We find that apart from incidental exceptions, the Kohn-Sham referenced CC methods show systematic deterioration compared to HF-CC, that is, the KS-CC molecular properties (electronic energy and density) are always farther from the FCI limit than those obtained from HF-CC at the same coupled cluster level. Furthermore, the introduction of common approximations (frozen core, density fitting) to the CC calculation results in significantly higher errors in the case of KS reference. We conclude that the use of KS reference orbitals is not expected to increase the reliability of low-level CC energetics. Nevertheless, molecular errors from the components of the studied chemical reaction might fortunately cancel out resulting in illusory improvement compared to HF-CC. It is also notable that the choice of reference orbitals has negligible influence on the results at sufficiently high CC levels which can be estimated by test calculations or by the magnitude of double amplitudes. Therefore, the application of KS-CC is not unreasonable as it might bypass the difficulties of HF convergence.

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