Efficient implementations of the symmetric and asymmetric triple excitation corrections for the orbital-optimized coupled-cluster doubles (OCCD) method with the density-fitting approach, denoted by DF-OCCD(T) and DF-OCCD(T)_Λ, are presented. The computational cost of the DF-OCCD(T) method is compared with that of the conventional OCCD(T). In the conventional OCCD(T) and OCCD(T)_Λ methods, one needs to perform four-index integral transformations at each coupled-cluster doubles iterations, which limits its applications to large chemical systems. Our results demonstrate that DF-OCCD(T) provides dramatically lower computational costs compared to OCCD(T), and there are more than 68-fold reductions in the computational time for the C₅H₁₂ molecule with the cc-pVTZ basis set. Our results show that the DF-OCCD(T) and DF-OCCD(T)_Λ methods are very helpful for the study of single bond-breaking problems. Performances of the DF-OCCD(T) and DF-OCCD(T)_Λ methods are noticeably better than that of the coupled-cluster singles and doubles with perturbative triples [CCSD(T)] method for the potential energy surfaces of the molecules considered. Specifically, the DF-OCCD(T)_Λ method provides dramatic improvements upon CCSD(T), and there are 8–14-fold reductions in nonparallelity errors. Overall, we conclude that the DF-OCCD(T)_Λ method is very promising for the study of challenging chemical systems, where the CCSD(T) fails.

中文翻译：

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使用密度拟合近似的轨道优化耦合簇双方法的对称和非对称三重激发校正的有效实现

介绍了使用密度拟合方法对轨道优化耦合簇双 (OCD) 方法进行对称和非对称三重激发校正的有效实现，用 DF-OCD(T) 和 DF-OCD(T) _Λ表示。DF-OCD(T) 方法的计算成本与传统 OCCD(T) 的计算成本进行了比较。在传统的 OCCD(T) 和 OCCD(T) _Λ方法中，需要在每个耦合簇双倍迭代中进行四指数积分变换，这限制了其在大型化学体系中的应用。我们的结果表明，与 OCCD(T) 相比，DF-OCD(T) 提供了显着降低的计算成本，并且 C ₅ H ₁₂的计算时间减少了 68 倍以上具有 cc-pVTZ 基组的分子。我们的结果表明，DF-OCD(T) 和 DF-OCD(T) _Λ方法对单键断裂问题的研究非常有帮助。对于所考虑分子的势能面，DF-OCD(T) 和 DF-OCD(T) _Λ方法的性能明显优于具有微扰三元组 [CCSD(T)] 方法的耦合簇单倍和双倍方法的性能. 具体来说，DF-OCD(T) _Λ方法对 CCSD(T) 提供了显着的改进，并且非平行误差减少了 8-14 倍。总的来说，我们得出结论，DF-OCD(T) _Λ方法对于研究具有挑战性的化学系统非常有前途，其中 CCSD(T) 失败。