Spin–flip non-orthogonal configuration interaction: a variational and almost black-box method for describing strongly correlated molecules

Mayhall, Nicholas J.; Horn, Paul R.; Sundstrom, Eric J.; Head‐Gordon, Martin

doi:10.1039/c4cp02818j

Cited by 53 publications

(79 citation statements)

References 93 publications

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“…In the following, we consider that the

Φ_{k}^{VB}

are known and only the

c_{k}^{}

need to be evaluated. The assumption that the

Φ_{k}^{VB}

are known makes sense if the VB orbitals can be somehow transferable from one system to another, and/or from some state to another state . Hence, the

Φ_{k}^{VB}

can be optimized independently from the targeted state, and used as building blocks for the wave function of a targeted state (ground or excited state).…”

Section: Methodsmentioning

confidence: 99%

“…The assumption that the F VB k are known makes sense if the VB orbitals can be somehow transferable from one system to another, and/or from some state to another state. [15,39] Hence, the F VB k can be optimized independently from the targeted state, and used as building blocks for the wave function of a targeted state (ground or excited state). If W MO and W VB describe the same state, we can write:…”

Section: Methodsmentioning

confidence: 99%

“…[1] All approaches in this field are based on the atomic concept. Density or charge analysis, [2][3][4][5][6] electronic density derivative analysis, [7][8][9][10][11][12] and even various energy decomposition analysis, [13][14][15] all reside on the ground of atomic objects, as centroids or as basins. Self consistent non orthogonal valence bond (VB) theory [16][17][18] and related approaches [19][20][21][22] also rely on atomic centroids, and among the variety of VB approaches, [23] we focused particularly on the first type of approaches, those that can define strictly localized orbitals.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Recasting wave functions into valence bond structures: A simple projection method to describe excited states

et al. 2016

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A method is proposed to obtain coefficients and weights of valence bond (VB) determinants from multi configurational wave functions. This reading of the wave functions can apply to ground states as well as excited states. The method is based on projection operators. Both energetic and overlap-based criteria are used to assess the quality of the resulting VB wave function. The approach gives a simple access to a VB rewriting for low-lying states, and it is applied to the allyl cation, to the allyl radical and to the ethene (notably to the V-state). For these states, large overlap between VB and multi reference wave functions are easily obtained. The approach proves to be useful to propose an interpretation of the nature of the V-state of ethene.

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“…In the following, we consider that the

Φ_{k}^{VB}

are known and only the

c_{k}^{}

need to be evaluated. The assumption that the

Φ_{k}^{VB}

are known makes sense if the VB orbitals can be somehow transferable from one system to another, and/or from some state to another state . Hence, the

Φ_{k}^{VB}

can be optimized independently from the targeted state, and used as building blocks for the wave function of a targeted state (ground or excited state).…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Recasting wave functions into valence bond structures: A simple projection method to describe excited states

et al. 2016

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“…4 This work has subsequently been extended to the calculation of multi-electron excitations 5 and core-excited states. 6,7 A method for describing strongly correlated systems based on defining a linear combination of determinants generated from all possible spin-flip excitations of a high spin restricted open-shell Hartree-Fock (ROHF) wave function and for which, independently, all non-active-space orbitals were allowed to relax, was proposed by Mayhall et al, 8 which avoids potential difficulties with converging excited states.…”

Section: Introductionmentioning

confidence: 99%

GronOR: Massively parallel and GPU-accelerated non-orthogonal configuration interaction for large molecular systems

Straatsma

Broer

Faraji

et al. 2020

The Journal of Chemical Physics

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“…25,26 For cases where the single-determinant representation fails, the utilisation of these multiple HF solutions as a basis for nonorthogonal con guration interaction (NOCI) has been shown to recover symmetry-pure multi-reference ground and excited state energies. 21,[27][28][29][30][31] Despite signi cant progress, however, our understanding of the general nature of multiple solutions remains surprisingly limited. 18,20,23,[31][32][33][34][35][36][37][38][39][40][41] In this Le er, we propose a totally novel approach for exploring multiple solutions in electronic structure methods.…”

mentioning

confidence: 99%

Complex adiabatic connection: A hidden non-Hermitian path from ground to excited states

2019

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Processes related to electronically excited states are central in many areas of science, however accurately determining excited-state energies remains a major challenge in theoretical chemistry. Recently, higher energy stationary states of non-linear methods have themselves been proposed as approximations to excited states, although the general understanding of the nature of these solutions remains surprisingly limited. In this Le er, we present an entirely novel approach for exploring and obtaining excited stationary states by exploiting the properties of non-Hermitian Hamiltonians. Our key idea centres on performing analytic continuations of conventional quantum chemistry methods. Considering Hartree-Fock theory as an example, we analytically continue the electron-electron interaction to expose a hidden connectivity of multiple solutions across the complex plane, revealing a close resemblance between Coulson-Fischer points and non-Hermitian degeneracies. Finally, we demonstrate how a ground-state wave function can be morphed naturally into an excited-state wave function by constructing a well-de ned complex adiabatic connection.Introduction.-Electronic excited states are central in chemistry, physics and biology, playing a role in key processes such as photochemistry, catalysis, and solar cell technology. However, de ning e ective methods that reliably provide accurate excited-state energies remains a major challenge in theoretical chemistry. Two of the most widely-used approaches to obtain excited-state energies are i) the time-dependent (TD) version of density-functional theory (DFT) which relies on the linear response formalism, and ii) the equation-of-motion (EOM) ansatz of coupled cluster (CC) theory.In particular, TD-DFT has practically revolutionised computational chemistry due to its user-friendly black-box nature compared with the more computationally expensive multi-con gurational methods (such as CASPT2 and NEVPT2) where one must choose an active space based on chemical intuition. Despite their success, fundamental de ciencies associated with TD-DFT and EOM-CC remain. For example, excited states presenting double excitation character 1-8 -which have a key role in the faithful description of many physical and chemical processes -are notoriously di cult to model using conventional single-reference methods such as adiabatic TD-DFT or EOM-CC. Although some viable and promising alternative approaches have been developed -for example spin-ip, 5 dressed TD-DFT 2 or ensemble DFT 6 -each faces major limitations.At present, most excited-state techniques, including TD-DFT and EOM-CC, are built upon a single reference Slater determinant, o en corresponding to a Hartree-Fock (HF) solution. As an inherently non-linear method, similar to CC 9 and GW, 10-17 HF can produce a multitude of distinct stationary states. In recent years, multiple HF states have themselves been proposed as approximations to excited states. [18][19][20][21] However, these solutions do not necessarily share the symmetries of the exact Hamilto...

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Spin–flip non-orthogonal configuration interaction: a variational and almost black-box method for describing strongly correlated molecules

Cited by 53 publications

References 93 publications

Recasting wave functions into valence bond structures: A simple projection method to describe excited states

Recasting wave functions into valence bond structures: A simple projection method to describe excited states

GronOR: Massively parallel and GPU-accelerated non-orthogonal configuration interaction for large molecular systems

Complex adiabatic connection: A hidden non-Hermitian path from ground to excited states

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