Projected Quasiparticle Theory for Molecular Electronic Structure

Abstract

We derive and implement symmetry-projected Hartree-Fock-Bogoliubov (HFB) equations and apply them to the molecular electronic structure problem. All symmetries (particle number, spin, spatial, and complex conjugation) are deliberately broken and restored in a self-consistent variation-after-projection approach. We show that the resulting method yields a comprehensive black-box treatment of strong correlations with effective one-electron (mean-field) computational cost. The ensuing wave function is of multireference character and permeates the entire Hilbert space of the problem. The energy expression is different from regular HFB theory but remains a functional of an independent quasiparticle density matrix. All reduced density matrices are expressible as an integration of transition density matrices over a gauge grid. We present several proof-of-principle examples demonstrating the compelling power of projected quasiparticle theory for electronic structure theory.

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Cited by in corpus (74)

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• Effective density functionals beyond mean field
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• Measuring Electron Correlation. The Impact of Symmetry and Orbital Transformations
• Local density approximation in site-occupation embedding theory
• Matrix elements of one-body and two-body operators between arbitrary HFB multi-quasiparticle states
• Configuration interaction combined with spin-projection for strongly correlated molecular electronic structures
• Exploring non-linear correlators on AGP
• Proper and improper zero energy modes in Hartree-Fock theory and their relevance for symmetry breaking and restoration
• Generalised Nonorthogonal Matrix Elements: Unifying Wick's Theorem and the Slater-Condon Rules
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• Construction of linearly independent non-orthogonal AGP states
• AGP-based unitary coupled cluster theory for quantum computers
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• Efficient computation of Hamiltonian matrix elements between non-orthogonal Slater determinants
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• Hartree-Fock symmetry breaking around conical intersections
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• General technique for analytical derivatives of post-projected Hartree-Fock
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• State preparation of AGP on a quantum computer without number projection
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• Global solutions of restricted open-shell Hartree-Fock theory from semidefinite programming with applications to strongly correlated quantum systems
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• Molecule-optimized Basis Sets and Hamiltonians for Accelerated Electronic Structure Calculations of Atoms and Molecules
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