Varandas A J C
School of Physics and Physical Engineering, Qufu Normal University, 273165 Qufu, China.
Phys Chem Chem Phys. 2021 Apr 22;23(15):9571-9584. doi: 10.1039/d1cp00357g.
Cost-effectiveness and accuracy are two basic pillars in electronic structure calculations. While cost-effectiveness enhances applicability, high accuracy is sustained when employing advanced computational tools. With the gold standard method of ab initio quantum chemistry at the focal point, canonical CCSD(T) and modern explicitly correlated CCSD(T)-F12 calculations are employed hand in hand to develop accurate hybrid post-CBS extrapolation schemes, which are validated using popular training sets involving a total of 130 molecules. By using raw valence-only calculations at CCSD(T)/VDZ and CCSD(T)/VQZ-F12 levels of theory, the novel scheme leads to the prediction of absolute energies that differ on average (-0.170 ± 0.224) kcal mol-1 from the highest affordable CCSD(T)-F12b/V(Q,5)Z-F12 extrapolations, but only (-0.048 ± 0.228) kcal mol-1 from the post-CBS extrapolated values based on CBS(D,T), CBS(D,Q) and CBS(T,Q) energies. From the cost-effectiveness standpoint, the approach is a kind of pseudo one-point extrapolation scheme since its cost is basically that of the highest-rung raw energy where it is based. Variants that imply no additional cost are also discussed, emerging h-pCBS(dt,dq)ab as the most effective. The approach can also be used with PNO-based local correlation methods that gained popularity due to allowing coupled-cluster calculations even for large molecules at reduced computational cost, namely local PNO-CCSD(T) and PNO-CCSD(T)-F12b. To gauge the approach performance, both the hydrogen molecule and the O-C2H5 torsion path of ethyl-methyl-ether, an extra molecule here considered with presupposed existence in astrophysical objects, are also studied. Additionally, the nonbonding interactions in the A24 test set are revisited per se. The results show that the title approach may be useful in high-accuracy quantum chemistry, with further improvements requiring the inclusion of contributions beyond the theory here employed such as the ones due to relativistic and nonadiabatic effects.
成本效益和准确性是电子结构计算的两个基本支柱。虽然成本效益提高了适用性，但在使用先进的计算工具时能保持高精度。以从头算量子化学的金标准方法为重点，同时采用规范的CCSD(T)和现代显式相关的CCSD(T)-F12计算来开发精确的混合后CBS外推方案，这些方案使用总共包含130个分子的流行训练集进行了验证。通过在CCSD(T)/VDZ和CCSD(T)/VQZ-F12理论水平上使用仅价层的原始计算，该新方案预测的绝对能量与最高可用的CCSD(T)-F12b/V(Q,5)Z-F12外推值平均相差(-0.170±0.224) kcal mol-1，但与基于CBS(D,T)、CBS(D,Q)和CBS(T,Q)能量的后CBS外推值仅相差(-0.048±0.228) kcal mol-1。从成本效益的角度来看，该方法是一种伪单点外推方案，因为其成本基本上是其所基于的最高级原始能量的成本。还讨论了不涉及额外成本的变体，其中新兴的h-pCBS(dt,dq)ab最为有效。该方法也可与基于PNO的局部相关方法一起使用，由于允许以降低的计算成本对大分子进行耦合簇计算，这些方法变得很流行，即局部PNO-CCSD(T)和PNO-CCSD(T)-F12b。为了评估该方法的性能，还研究了氢分子以及乙基甲基醚的O-C2H5扭转路径，这里额外考虑了一个假设存在于天体物理对象中的分子。此外，还单独重新研究了A24测试集中的非键相互作用。结果表明，本文所述方法可能在高精度量子化学中有用，进一步的改进需要纳入本文所采用理论之外的贡献，例如相对论和非绝热效应引起的贡献。
