Grabowski Ireneusz, Lotrich Victor, Bartlett Rodney J
Institute of Physics, Nicolaus Copernicus University, 87-100 Toruń, Poland.
J Chem Phys. 2007 Oct 21;127(15):154111. doi: 10.1063/1.2790013.
Ab initio density functional theory (DFT), previously applied primarily at the second-order many-body perturbation theory (MBPT) level, is generalized to selected infinite-order effects by using a new coupled-cluster perturbation theory (CCPT). This is accomplished by redefining the unperturbed Hamiltonian in ab initio DFT to correspond to the CCPT2 orbital dependent functional. These methods are applied to the Be-isoelectronic systems as an example of a quasidegenerate system. The CCPT2 variant shows better convergence to the exact quantum Monte Carlo correlation potential for Be than any prior attempt. When using MBPT2, the semicanonical choice of unperturbed Hamiltonian, plays a critical role in determining the quality of the obtained correlation potentials and obtaining convergence, while the usual Kohn-Sham choice invariably diverges. However, without the additional infinite-order effects, introduced by CCPT2, the final potentials and energies are not sufficiently accurate. The issue of the effects of the single excitations on the divergence in ordinary OEP2 is addressed, and it is shown that, whereas their individual values are small, their infinite-order summation is essential to the good convergence of ab initio DFT.
从头算密度泛函理论（DFT），此前主要应用于二阶多体微扰理论（MBPT）水平，通过使用一种新的耦合簇微扰理论（CCPT）推广到选定的无穷阶效应。这是通过将从头算DFT中的未微扰哈密顿量重新定义为与CCPT2轨道依赖泛函相对应来实现的。这些方法应用于Be等电子体系，作为准简并体系的一个例子。CCPT2变体比任何先前的尝试都能更好地收敛到Be的精确量子蒙特卡罗相关势。当使用MBPT2时，未微扰哈密顿量的半规范选择在确定所获得的相关势的质量和实现收敛方面起着关键作用，而通常的Kohn-Sham选择总是发散。然而，没有CCPT2引入的额外无穷阶效应，最终的势和能量就不够精确。研究了单激发对普通OEP2中发散的影响问题，结果表明，虽然它们的单个值很小，但它们的无穷阶求和对于从头算DFT的良好收敛至关重要。
