QuantNBody: a Python package for quantum chemistry and
physics to build and manipulate many-body operators and wave
functions.

Yalouz, Saad; Gullin, Martin Rafael; Sekaran, Sajanthan

doi:10.21105/joss.04759

Cited by 4 publications

(2 citation statements)

References 12 publications

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“…All numerical implementations and calculations presented in this paper were carried out within the python package QuantNBody (see ref 22) recently developed by one of us (S.Y.). This package was designed to facilitate the numerical implementation of second quantization algebra and the manipulation of many-body wave functions.…”

Section: ■ Numerical Resultsmentioning

confidence: 99%

Orthogonally Constrained Orbital Optimization: Assessing Changes of Optimal Orbitals for Orthogonal Multireference States

Yalouz

Robert

2023

J. Chem. Theory Comput.

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The choice of molecular orbitals is decisive in configuration interaction calculations. In this letter, a democratic description of the ground and excited states follows an orthogonally constrained orbital optimization to produce state-specific orbitals. The approach faithfully recovers the excitation energy of a fourelectron Hubbard trimer, whereas state-average calculations can miss the value by a factor 2.5. The method emphasizes the need for orbital optimization to reduce configuration interaction expansions and to reach spectroscopic accuracy.

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Section: ■ Numerical Resultsmentioning

confidence: 99%

Orthogonally Constrained Orbital Optimization: Assessing Changes of Optimal Orbitals for Orthogonal Multireference States

Yalouz

Robert

2023

J. Chem. Theory Comput.

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“…This procedure allows for a decomposition into the different entangled metal–ligand contributions. To implement these projections and conduct our local spin analysis, the open access package QuantNBody was used. This numerical python toolbox has been recently developed by one of us (SY) to facilitate the manipulation of quantum many-body operators and wave functions.…”

Section: Computational Detailsmentioning

confidence: 99%

Modifications of Tanabe-Sugano d⁶ Diagram Induced by Radical Ligand Field: Ab Initio Inspection of a Fe(II)-Verdazyl Molecular Complex

et al. 2023

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Quantum entanglement between the spin states of a metal center and radical ligands is suggested in an iron(II) [Fe(dipyvd)2]2+ compound (dipyvd = 1-isopropyl-3,5-dipyridil-6-oxoverdazyl). Wave function ab initio (Difference Dedicated Configuration Interaction, DDCI) inspections were carried out to stress the versatility of local spin states. We named this phenomenon excited state spinmerism, in reference to our previous work (see Roseiro et al., ChemPhysChem 2022, e202200478) where we introduced the concept of spinmerism as an extension of mesomerism to spin degrees of freedom. The construction of localized molecular orbitals allows for a reading of the wave functions and projections onto the local spin states. The low-energy spectrum is well-depicted by a Heisenberg picture. A 60 cm–1 ferromagnetic interaction is calculated between the radical ligands with the S total = 0 and 1 states largely dominated by a local low-spin S Fe = 0. In contrast, the higher-lying S total = 2 states are superpositions of the local S Fe = 1 (17%, 62%) and S Fe = 2 (72%, 21%) spin states. Such mixing extends the traditional picture of a high-field d 6 Tanabe-Sugano diagram. Even in the absence of spin–orbit coupling, the avoided crossing between different local spin states is triggered by the field generated by radical ligands. This puzzling scenario emerges from versatile local spin states in compounds which extend the traditional views in molecular magnetism.

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A unified density matrix functional construction of quantum baths in density matrix embedding theory beyond the mean-field approximation

Sekaran

Bindech

Fromager

2023

The Journal of Chemical Physics

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The equivalence in one-electron quantum baths between the practical implementation of density matrix embedding theory (DMET) and the more recent Householder-transformed density matrix functional embedding theory has been shown previously in the standard but special case where the reference full-size (one-electron reduced) density matrix, from which the bath is constructed, is idempotent [S. Yalouz et al., J. Chem. Phys. 157, 214112 (2022)]. We prove mathematically that the equivalence remains valid when the density matrix is not idempotent anymore, thus allowing for the construction of correlated (one-electron) quantum baths. A density-matrix functional exactification of DMET is derived within the present unified quantum embedding formalism. Numerical examples reveal that the embedding cluster can be quite sensitive to the level of density-matrix functional approximation used for computing the reference density matrix.

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QuantNBody: a Python package for quantum chemistry and physics to build and manipulate many-body operators and wave functions.

Cited by 4 publications

References 12 publications

Orthogonally Constrained Orbital Optimization: Assessing Changes of Optimal Orbitals for Orthogonal Multireference States

Orthogonally Constrained Orbital Optimization: Assessing Changes of Optimal Orbitals for Orthogonal Multireference States

Modifications of Tanabe-Sugano d⁶ Diagram Induced by Radical Ligand Field: Ab Initio Inspection of a Fe(II)-Verdazyl Molecular Complex

A unified density matrix functional construction of quantum baths in density matrix embedding theory beyond the mean-field approximation

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QuantNBody: a Python package for quantum chemistry and physics to build and manipulate many-body operators and wave functions.

Cited by 4 publications

References 12 publications

Orthogonally Constrained Orbital Optimization: Assessing Changes of Optimal Orbitals for Orthogonal Multireference States

Orthogonally Constrained Orbital Optimization: Assessing Changes of Optimal Orbitals for Orthogonal Multireference States

Modifications of Tanabe-Sugano d6 Diagram Induced by Radical Ligand Field: Ab Initio Inspection of a Fe(II)-Verdazyl Molecular Complex

A unified density matrix functional construction of quantum baths in density matrix embedding theory beyond the mean-field approximation

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Product

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Modifications of Tanabe-Sugano d⁶ Diagram Induced by Radical Ligand Field: Ab Initio Inspection of a Fe(II)-Verdazyl Molecular Complex