Department of Chemistry and Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892, USA.
J Chem Phys. 2013 Dec 21;139(23):234113. doi: 10.1063/1.4848075.
The accurate and efficient description of strong electronic correlations remains an important objective in electronic structure theory. Projected Hartree-Fock theory, where symmetries of the Hamiltonian are deliberately broken and projectively restored, all with a mean-field computational scaling, shows considerable promise in this regard. However, the method is neither size extensive nor size consistent; in other words, the correlation energy per particle beyond broken-symmetry mean field vanishes in the thermodynamic limit, and the dissociation limit of a molecule is not the sum of the fragment energies. These two problems are closely related. Recently, Neuscamman [Phys. Rev. Lett. 109, 203001 (2012)] has proposed a method to cure the lack of size consistency in the context of the antisymmetrized geminal power wave function (equivalent to number-projected Hartree-Fock-Bogoliubov) by using a Jastrow-type correlator in Hilbert space. Here, we apply the basic idea in the context of projected Hartree-Fock theory, linearizing the correlator for computational simplicity but extending it to include spin fluctuations. Results are presented for the Hubbard Hamiltonian and for some simple molecular systems.
准确而有效地描述强电子相关仍然是电子结构理论的一个重要目标。投影 Hartree-Fock 理论，其中哈密顿量的对称性被故意打破并投影恢复，所有这些都具有平均场计算尺度，在这方面显示出相当大的前景。然而，该方法既不是大小扩展性的，也不是大小一致性的；换句话说，超出破对称平均场的每粒子相关能量在热力学极限中消失，并且分子的离解极限不是碎片能量的总和。这两个问题密切相关。最近，Neuscamman [Phys. Rev. Lett. 109, 203001 (2012)]提出了一种方法，通过在 Hilbert 空间中使用 Jastrow 型相关器来治疗反对称双子幂次波函数（相当于数投影 Hartree-Fock-Bogoliubov）中缺乏大小一致性的问题。在这里，我们将基本思想应用于投影 Hartree-Fock 理论中，通过线性化相关器来简化计算，但将其扩展到包括自旋涨落。结果显示在 Hubbard 哈密顿量和一些简单的分子系统中。
