School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210093, People's Republic of China.
J Chem Phys. 2012 Jan 28;136(4):044101. doi: 10.1063/1.3678008.
We have proposed a simple strategy for splitting the virtual orbitals with a large basis set into two subgroups (active and inactive) by taking a smaller basis set as an auxiliary basis set. With the split virtual orbitals (SVOs), triple or higher excitations can be partitioned into active and inactive subgroups (according to the number of active virtual orbitals involved), which can be treated with different electron correlation methods. In this work, the coupled cluster (CC) singles, doubles, and a hybrid treatment of connected triples based on the SVO [denoted as SVO-CCSD(T)-h], has been implemented. The present approach has been applied to study the bond breaking potential energy surfaces in three molecules (HF, F(2), and N(2)), and the equilibrium properties in a number of open-shell diatomic molecules. For all systems under study, the SVO-CCSD(T)-h method based on the unrestricted Hartree-Fock (UHF) reference is an excellent approximation to the corresponding CCSDT (CC singles, doubles, and triples), and much better than the UHF-based CCSD(T) (CC singles, doubles, and perturbative triples). On the other hand, the SVO-CCSD(T)-h method based on the restricted HF (RHF) reference can also provide considerable improvement over the RHF-based CCSD(T).
我们提出了一种简单的策略，通过使用较小的基组作为辅助基组，将具有大基组的虚拟轨道分为两个子组（活动和非活动）。使用分裂虚拟轨道（SVOs），可以将三电子或更高激发态分为活动和非活动子组（根据涉及的活动虚拟轨道的数量），可以用不同的电子相关方法处理。在这项工作中，实现了基于 SVOs 的耦合簇（CC）单电子、双电子和连接三电子的混合处理[表示为 SVO-CCSD(T)-h]。本方法已应用于研究三个分子（HF、F₂ 和 N₂）中的键断裂势能面以及若干开壳层双原子分子中的平衡性质。对于所有研究的体系，基于非限制哈特ree-fock（UHF）参考的 SVO-CCSD(T)-h 方法是对相应 CCSDT（CC 单电子、双电子和三电子）的极好近似，并且比基于 UHF 的 CCSD(T)（CC 单电子、双电子和微扰三电子）要好得多。另一方面，基于限制哈特ree-fock（RHF）参考的 SVO-CCSD(T)-h 方法也可以对基于 RHF 的 CCSD(T) 提供相当大的改进。
