Influence of broken-pair excitations on the exact pair wavefunction

Abstract

Doubly occupied configuration interaction (DOCI), the exact diagonalization of the Hamiltonian in the paired (seniority zero) sector of the Hilbert space, is a combinatorial cost wave function that can be very efficiently approximated by pair coupled cluster doubles (pCCD) at mean-field computational cost. As such, it is a very interesting candidate as a starting point for building the full configuration interaction (FCI) ground state eigenfunction belonging to all (not just paired) seniority sectors. The true seniority zero sector of FCI (referred to here as FCI${}_0$) includes the effect of coupling between all seniority sectors rather than just seniority zero, and is, in principle, different from DOCI. We here study the accuracy with which DOCI approximates FCI${}_0$. Using a set of small Hubbard lattices, where FCI is possible, we show that DOCI $\sim$ FCI${}_0$ under weak correlation. However, in the strong correlation regime, the nature of the FCI${}_0$ wavefunction can change significantly, rendering DOCI and pCCD a less than ideal starting point for approximating FCI.

References in corpus (10)

• Seniority-based coupled cluster theory
• Efficient description of strongly correlated electrons with mean-field cost
• Quasiparticle Coupled Cluster Theory for Pairing Interactions
• Symmetry in Auxiliary-Field Quantum Monte Carlo Calculations
• Linearized Coupled Cluster Correction on the Antisymmetric Product of 1 reference orbital Geminals
• Pair extended coupled cluster doubles
• Polynomial Similarity Transformation Theory: A smooth interpolation between coupled cluster doubles and projected BCS applied to the reduced BCS Hamiltonian
• Symmetry-projected Wave Functions in Quantum Monte Carlo Calculations
• Using full configuration interaction quantum Monte Carlo in a seniority zero space to investigate the correlation energy equivalence of pair coupled cluster doubles and doubly occupied configuration interaction
• Projected Hartree Fock Theory as a Polynomial Similarity Transformation Theory of Single Excitations

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• Geminal replacement models based on AGP
• The seniority quantum number in Tensor Network States
• Correlated pair ansatz with a binary tree structure
• Jordan-Wigner Transformation for the Description of Strong Correlation in Fermionic Systems
• Near-exact treatment of seniority-zero ground and excited states with a Richardson-Gaudin mean-field