Gwaltney Steven R
Department of Chemistry, Center for Environmental Health Sciences, and Center for Computational Sciences, Mississippi State University, Mississippi State, Mississippi 39762, United States.
J Phys Chem A. 2024 Oct 17;128(41):9055-9062. doi: 10.1021/acs.jpca.4c04910. Epub 2024 Oct 7.
Coupled-cluster singles and doubles calculations with perturbative triples [CCSD(T)] offer high accuracy with significant cost. The standard way to reduce the cost of a CCSD(T) calculation is by excluding molecular orbitals from the correlated calculation. While this speeds up the calculation, it also throws away the contribution from the inactive orbitals to the correlation energy. Here, we propose extending the standard CCSD(T) method to account for the effects of these inactive orbitals. This approach is based on a perturbation expansion of the similarity-transformed Hamiltonian, and the final method includes external singles and doubles corrections along with a semi-internal triples term. Compared to all-electron CCSD(T) calculations with the cc-pCVTZ basis set for a set of small molecules, we recovered, on average, 98% of the total correlation energy while using only 30% of the molecular orbitals. Using 72% of the molecular orbitals gave 99.5% of the correlation energy.
含微扰三重激发的耦合簇单双激发计算[CCSD(T)]能提供高精度，但成本高昂。降低CCSD(T)计算成本的标准方法是在相关计算中排除分子轨道。虽然这加快了计算速度，但也舍弃了非活性轨道对相关能的贡献。在此，我们提议扩展标准CCSD(T)方法以考虑这些非活性轨道的影响。该方法基于相似变换哈密顿量的微扰展开，最终方法包括外部单双激发校正以及一个半内部三重激发项。与使用cc-pCVTZ基组对一组小分子进行的全电子CCSD(T)计算相比，我们平均仅使用30%的分子轨道就恢复了总相关能的98%。使用72%的分子轨道则可得到99.5%的相关能。
