Department of Chemistry, Washington State University, Pullman, Washington 99164, USA.
J Chem Phys. 2010 Nov 14;133(18):184102. doi: 10.1063/1.3491809.
Explicitly correlated CCSD(T)-F12a/b methods combined with basis sets specifically designed for this technique have been tested for their ability to reproduce standard CCSD(T) benchmark data covering 16 small molecules composed of hydrogen and carbon. The standard method calibration set was obtained with very large one-particle basis sets, including some aug-cc-pV7Z and aug-cc-pV8Z results. Whenever possible, the molecular properties (atomization energies, structures, and harmonic frequencies) were extrapolated to the complete basis set limit in order to facilitate a direct comparison of the standard and explicitly correlated approaches without ambiguities arising from the use of different basis sets. With basis sets of triple-ζ quality or better, the F12a variant was found to overshoot the presumed basis set limit, while the F12b method converged rapidly and uniformly. Extrapolation of F12b energies to the basis set limit was found to be very effective at reproducing the best standard method atomization energies. Even extrapolations based on the small cc-pVDZ-F12/cc-pVTZ-F12 combination proved capable of a mean absolute deviation of 0.20 kcal/mol. The accuracy and simultaneous cost savings of the F12b approach are such that it should enable high quality property calculations to be performed on chemical systems that are too large for standard CCSD(T).
经过测试，专门设计用于该技术的显式相关 CCSD(T)-F12a/b 方法与基组相结合，能够重现涵盖 16 个由氢和碳组成的小分子的标准 CCSD(T)基准数据。标准方法校准集是使用非常大的单粒子基组获得的，包括一些 aug-cc-pV7Z 和 aug-cc-pV8Z 的结果。只要有可能，就将分子性质（原子化能、结构和调和频率）外推到完全基组极限，以便在没有使用不同基组引起歧义的情况下直接比较标准和显式相关方法。在三 ζ 质量或更好的基组上，发现 F12a 变体超过了假定的基组极限，而 F12b 方法则快速且一致地收敛。发现 F12b 能量外推到基组极限对于重现最佳标准方法原子化能非常有效。即使基于小的 cc-pVDZ-F12/cc-pVTZ-F12 组合的外推也能够将平均绝对偏差控制在 0.20 kcal/mol 以内。F12b 方法的准确性和同时节省成本使得它能够对太大而无法进行标准 CCSD(T)的化学系统进行高质量的性质计算。
