论文标题
具有四倍激动的近似耦合群集方法的分析梯度
Analytic Gradients of Approximate Coupled Cluster Methods with Quadruple Excitations
论文作者
论文摘要
介绍了包括连接四倍激发的迭代和非迭代耦合群集近似值的分析梯度理论。这些方法特别包括CCSDT（Q），它是众所周知的CCSD（T）方法的类似物，该方法从完整的CCSDT方法而不是CCSD开始。所得的方法是在CFOUR程序套件中实现的，并为最简单的Criegee中间体的平衡几何形状和谐波振动频率提出了试点应用，以及CH $ _2 $ OO，以及Dimethylization途径之间的异构化途径。尽管所有方法都可以近似于“行为良好”系统的完整CCSDTQ结果，但是Criegee中间体的更困难的情况表明CCSDT（Q）以及某些迭代近似值，表现出有问题的行为。
The analytic gradient theory for both iterative and non-iterative coupled-cluster approximations that include connected quadruple excitations is presented. These methods include, in particular, CCSDT(Q), which is an analog of the well-known CCSD(T) method which starts from the full CCSDT method rather than CCSD. The resulting methods are implemented in the CFOUR program suite, and pilot applications are presented for the equilibrium geometries and harmonic vibrational frequencies of the simplest Criegee intermediate, CH$_2$OO, as well as to the isomerization pathway between dimethylcarbene and propene. While all methods are seen to approximate the full CCSDTQ results well for "well-behaved" systems, the more difficult case of the Criegee intermediate shows that CCSDT(Q), as well as certain iterative approximations, display problematic behavior.
