Henderson Thomas M, Bulik Ireneusz W, Scuseria Gustavo E
Department of Chemistry, Rice University, Houston, Texas 77005-1892, USA.
J Chem Phys. 2015 Jun 7;142(21):214116. doi: 10.1063/1.4921986.
The accurate and efficient description of strongly correlated systems remains an important challenge for computational methods. Doubly occupied configuration interaction (DOCI), in which all electrons are paired and no correlations which break these pairs are permitted, can in many cases provide an accurate account of strong correlations, albeit at combinatorial computational cost. Recently, there has been significant interest in a method we refer to as pair coupled cluster doubles (pCCD), a variant of coupled cluster doubles in which the electrons are paired. This is simply because pCCD provides energies nearly identical to those of DOCI, but at mean-field computational cost (disregarding the cost of the two-electron integral transformation). Here, we introduce the more complete pair extended coupled cluster doubles (pECCD) approach which, like pCCD, has mean-field cost and reproduces DOCI energetically. We show that unlike pCCD, pECCD also reproduces the DOCI wave function with high accuracy. Moreover, pECCD yields sensible albeit inexact results even for attractive interactions where pCCD breaks down.
对于计算方法而言，准确且高效地描述强关联系统仍然是一项重大挑战。双占据组态相互作用（DOCI），即所有电子都成对且不允许有破坏这些对的关联，在许多情况下能够准确描述强关联，尽管其计算成本是组合式的。最近，人们对一种我们称为对耦合簇双激发（pCCD）的方法产生了浓厚兴趣，它是耦合簇双激发的一种变体，其中电子是成对的。这仅仅是因为pCCD提供的能量与DOCI的能量几乎相同，但计算成本仅为平均场成本（忽略双电子积分变换的成本）。在此，我们引入更完整的对扩展耦合簇双激发（pECCD）方法，它与pCCD一样具有平均场成本，并且在能量上能重现DOCI。我们表明，与pCCD不同，pECCD还能高精度地重现DOCI波函数。此外，即使对于pCCD失效的吸引相互作用，pECCD也能给出合理但不精确的结果。
