Geminal Approach

Śurján, Péter R.

doi:10.1016/b978-0-12-409547-2.11468-4

Cited by 4 publications

(3 citation statements)

References 92 publications

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“…Notable wave functions of the SLG class comprise generalized valence bond perfect pairing (GVB-PP), antisymmetrized product of strongly orthogonal geminals (APSG), ,− unrestricted Hartree–Fock (UHF), , restricted unrestricted singlet type strongly orthogonal geminals (RUSSG), and unrestriction in active pairs (UAP) . Of these, GVB-PP and APSG involve singlet-only geminals, leading to spin pure overall function, while UHF, RUSSG, and UAP are built with unrestricted geminals, yielding a function of the type of eq , spin contaminated in general.…”

Section: Theorymentioning

confidence: 99%

Half-Projection of the Strongly Orthogonal Unrestricted Geminals’ Product Wave Function

Mihálka

Śurján

Szabados

2019

J. Chem. Theory Comput.

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Half-projection of a wave function built as a product of singlet−triplet mixed two-electron fragments (geminals) is explored. The condition of strong orthogonality is imposed between geminals, the initial Ansatz accommodating the unrestricted Hartree−Fock (UHF) wave function as a special case. The here explored geminal product is more general than UHF, it allowing for single covalent bond breaking in a spin pure manner. The strong correlation present in two geminals simultaneously is accompanied by spin contamination at the geminal product level. Variation after half-projection leads to an eigenvalue problem of an effective two-electron Hamiltonian, conserving the computational economy of the initial model. While the resulting expressions are shown to violate size consistency, quantification reveals a suppressed error with half-projection as compared to the full spin projected then varied scheme. Spin contamination is also found to be diminished compared to the initial, unprojected wave function.

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Section: Theorymentioning

confidence: 99%

Half-Projection of the Strongly Orthogonal Unrestricted Geminals’ Product Wave Function

Mihálka

Śurján

Szabados

2019

J. Chem. Theory Comput.

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“…Several wave functions represent a special case of the SLG family; UHF and GVB-PP are the most widely known among these. Antisymmetrized Product of Strongly Orthogonal Geminals (APSG), ,− UAP, and RUSSG also belong to this category. A comparative account on these models is given, e.g., in ref .…”

Section: Theorymentioning

confidence: 99%

Symmetry-Adapted Perturbation with Half-Projection for Spin Unrestricted Geminals

Mihálka

Śurján

Szabados

2021

J. Chem. Theory Comput.

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Perturbative correction to a wave function built from singlet−triplet mixed two-electron functions (geminals) is derived in the context of symmetry-adapted schemes, applying partial spinprojection. Imposing the constraint of strong orthogonality of geminals results in a reference function that captures static correlation in a computationally feasible way. In case of a lack of spin purification, the product of spin-unrestricted geminals is generally spincontaminated, potentially undermining performance of a subsequent dynamic correlation treatment. In this work, spin symmetry of the reference is partially restored by half-projection in a variation-afterprojection scheme. Applying perturbation theory (PT) to recover the missing part of electron correlation is hampered by the fact that an obvious choice for a zero-order Hamiltonian is not provided. The situation is amended by adopting the formalism of symmetryadapted PT. The resulting framework is tested on singlet−triplet gaps of biradicaloids, and it is found to perform well in situations where its unprojected counterpart fails because of spin contamination.

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“…More details on this subject with an extensive list of references can be found in Refs. [40][41][42][43].…”

Section: Geminal Wave Functionsmentioning

confidence: 99%

Dressing of Interaction Verticles in Multi-Reference Coupled Cluster Theory

Margócsy¹

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Geminal Approach

Cited by 4 publications

References 92 publications

Half-Projection of the Strongly Orthogonal Unrestricted Geminals’ Product Wave Function

Half-Projection of the Strongly Orthogonal Unrestricted Geminals’ Product Wave Function

Symmetry-Adapted Perturbation with Half-Projection for Spin Unrestricted Geminals

Dressing of Interaction Verticles in Multi-Reference Coupled Cluster Theory

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