Lehrstuhl für Theoretische Chemie, Universität Bonn, Wegelerstr. 12, D-53115 Bonn, Germany.
J Chem Phys. 2011 Aug 28;135(8):084102. doi: 10.1063/1.3624567.
A strictly size extensive post-Hartree-Fock correlation functional being invariant with respect to orbital transformations within the occupied and virtual subspaces is presented. While avoiding the necessity to solve additional Z vector equations for the calculation of properties and energy gradients, this functional reproduces almost exactly the results of coupled-cluster singles doubles (CCSD) calculations. In particular, it is demonstrated that the method is rigorous in the sense that it can be systematically improved by the perturbative inclusion of triple excitations in the same way as CCSD. As to the computational cost, the presented approach is somewhat more expensive than the CCSD if the energy is variationally optimized with respect to both the orbitals and the excitation amplitudes. Replacement of orbital optimization by the Brueckner condition reduces the computational cost by a factor of two, thus making the method less expensive than CCSD.
本文提出了一种严格的、大小扩展性的、后哈特ree-fock 相关泛函，它在占据和虚拟子空间内的轨道变换方面是不变的。该泛函避免了为计算性质和能量梯度而求解额外的 Z 矢量方程的必要性，几乎完全再现了耦合簇单双激发（CCSD）计算的结果。特别是，证明了该方法是严格的，因为可以通过在相同的方式中用三激发的微扰包含来系统地改进它，就像 CCSD 一样。至于计算成本，如果能量是针对轨道和激发幅度进行变分优化的，那么与 CCSD 相比，所提出的方法会稍微昂贵一些。通过 Brueckner 条件替换轨道优化可以将计算成本降低一半，从而使该方法比 CCSD 更便宜。
