Communication: Hartree-Fock description of excited states of H2

Barca, Giuseppe M. J.; Gilbert, Andrew T. B.; Gill, Peter M. W.

doi:10.1063/1.4896182

Cited by 65 publications

(97 citation statements)

References 33 publications

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“…Despite these stumbling blocks, the Hartree-Fock method has been extended for excited states in various forms and their solutions are found to be useful as first-order approximations for the correlated excited state wavefunctions. [6][7][8][9] As a step forward, here, we establish that once the zeroth order closed-shell solutions using the ESHF method is available, the existing EOMCC approach is capable of computing the entire ground state potential energy curves of higher-order bonds with correct dissociation behavior. Further development of this approach is in progress which also include the development of an ESHF method for more complicated hetero-atomic systems.…”

Section: Discussionmentioning

confidence: 99%

“…Hence, the suitability of the EOMCC method for computing the entire ground state potential energy curve of higher-order bond has never been explored. In this article, we propose that the EOMCC method which is built over a closed-shell excited state Hartree-Fock (ESHF) [6][7][8][9] wavefunction is a straight forward approach for computing the entire ground state electronic potential energy curves (or binding energy curves) of higher-order bonds. Since the proposed EOMCC approach is built over the ESHF solutions, we refer to this approach as ESHF-EOMCC approach.…”

Section: Introductionmentioning

confidence: 99%

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EOMCC over excited state Hartree-Fock solutions (ESHF-EOMCC): An efficient approach for the entire ground state potential energy curves of higher-order bonds

Sajeev

2015

AIP Advances

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The equation-of-motion coupled cluster (EOMCC) method based on the excited state Hartree-Fock (ESHF) solutions is shown to be appropriate for computing the entire ground state potential energy curves of strongly correlated higher-order bonds. The new approach is best illustrated for the homolytic dissociation of higher-order bonds in molecules. The required multireference character of the true ground state wavefunction is introduced through the linear excitation operator of the EOMCC method. Even at the singles and doubles level of cluster excitation truncation, the nonparallelity error of the ground state potential energy curve from the ESHF based EOMCC method is small. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

EOMCC over excited state Hartree-Fock solutions (ESHF-EOMCC): An efficient approach for the entire ground state potential energy curves of higher-order bonds

Sajeev

2015

AIP Advances

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“…Importantly, and unlike previous work on excited states using unrestricted Hartree-Fock theory, 69 we adopt a spin-restricted framework, i.e., spinors have an equal spatial component for either up ↑ or down ↓ singleparticle states, thereby avoiding any symmetry breaking. Thus our ensembles account for eigenstates of bothŜ 2 andŜ z .…”

Section: A Numerically Solvable Model Of Ct Excitationsmentioning

confidence: 99%

Charge transfer excitations from exact and approximate ensemble Kohn-Sham theory

Gould¹,

Pittalis²,

Kronik³

2018

Preprint

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By studying the lowest excitations of an exactly solvable one-dimensional molecular model, we show that components of Kohn-Sham ensembles can be used to describe charge transfers. Furthermore, we compute the approximate excitation energies obtained by using thee exact ensemble densities in the recently formulated ensemble Hartree-exchange theory [Gould and Pittalis, Phys. Rev. Lett. 119, 243001 (2017)]. Remarkably, our results show that triplet excitations are accurately reproduced across a dissociation curve in all cases tested, even in systems where ground state energies are poor due to strong static correlations. Singlet excitations exhibit larger deviations from exact results but are still reproduced semi-quantitatively.

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“…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 Hamiltonian, 22,23 and the onset of symmetry breaking, where multiple solutions coalesce at so-called…”

mentioning

confidence: 99%

“…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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Communication: Hartree-Fock description of excited states of H2

Cited by 65 publications

References 33 publications

EOMCC over excited state Hartree-Fock solutions (ESHF-EOMCC): An efficient approach for the entire ground state potential energy curves of higher-order bonds

EOMCC over excited state Hartree-Fock solutions (ESHF-EOMCC): An efficient approach for the entire ground state potential energy curves of higher-order bonds

Charge transfer excitations from exact and approximate ensemble Kohn-Sham theory

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

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