Targeting excited states in all-trans polyenes with electron-pair states

Boguslawski, Katharina

doi:10.1063/1.4972053

Cited by 48 publications

(48 citation statements)

References 102 publications

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“…It is well known that such bi‐excited states cannot be correctly described by the standard (single‐reference) EOM‐CCSD framework. Recent work on all‐trans polyene chains highlights the superiority of EOM‐pCCD‐based methods to correctly describe double electron excitation energies . The same is true for the

^{1} Σ_{g}^{+}

excited state in the Yb 2 dimer.…”

Section: Resultsmentioning

confidence: 97%

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Modeling the electronic structures of the ground and excited states of the ytterbium atom and the ytterbium dimer: A modern quantum chemistry perspective

Tecmer

Boguslawski

Borkowski

et al. 2019

Int J of Quantum Chemistry

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We present a comprehensive theoretical study of the electronic structures of the Yb atom and the Yb 2 molecule, respectively, focusing on their ground and lowest-lying electronically excited states. Our study includes various state-of-the-art quantum chemistry methods such as CCSD, CCSD(T), CASPT2 (including spin-orbit coupling), and EOM-CCSD as well as some recently developed pCCD-based approaches and their extensions to target excited states. Specifically, we scan the lowest-lying potential energy surfaces of the Yb 2 dimer and provide a reliable benchmark set of spectroscopic parameters including optimal bond lengths, vibrational frequencies, potential energy depths, and adiabatic excitation energies. Our in-depth analysis unravels the complex nature of the electronic spectrum of Yb 2 , which is difficult to model accurately by any conventional quantum chemistry method. Finally, we scrutinize the biexcited character of the first 1 Σ + g excited state and its evolution along the potential energy surface. K E Y W O R D S relativistic effects, electron corellation effects, spin-orbit coupling, equation of motion coupled cluster, CASPT2 | INTRODUCTIONThe divalent ytterbium atom has in recent years garnered significant attention thanks to its many uses in cold atom physics. It has a nonmagnetic 1 S 0 ground state and several useful optical transitions: the strong 1 S 0 $ 1 P 1 line can be used for Zeeman slowing, whereas the narrow (181 kHz) intercombination 1 S 0 $ 3 P 1 line can be used to directly laser cool Yb atoms to microkelvin temperatures. [1] Yb has seven stable isotopes: two fermions (171 and 173 with nuclear spins of 1/2 and 5/2, respectively) and five bosons (168, 170, 172, 174, and 176) that lack nuclear spin. The rich isotope structure makes it possible to mass-tune the atomic interactions [2] and facilitates a wide array of possible quantum-degenerate gases. [3][4][5][6] The doubly forbidden 1 S 0 $ 3 P 0 transition lies at the heart of optical atomic clocks [7] that are among the most precise physical instruments known to mankind. For example, an ytterbium clock has recently been demonstrated to enable geopotential measurements with an accuracy below a centimeter. [8] The long-lived 3 P 0 clock states also find use in quantum simulations using Yb atoms. [9] The long-range interactions in the Yb dimer have been probed extensively by high-resolution photoassociation spectroscopy (PAS) [10] near the narrow 1 S 0 $ 3 P 1 intercombination line. The excited 1 S 0 + 3 P 1 (0 + u ) [11,12] state has been probed by single color PAS and provided the van der Waals C 6 coefficient and an improved value of the atomic 3 P 1 lifetime. Two-color PAS of ground state 0 + g vibrational levels [2,13] delivered accurate

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^{1} Σ_{g}^{+}

excited state in the Yb 2 dimer.…”

Section: Resultsmentioning

confidence: 97%

“…Single excitations were included a posteriori in the EOM ansatz, that is, the linear excitation operator of the EOM formalism is limited to pair and single excitations. This approach is denoted as EOM‐pCCD+S . The second model includes single excitations also in the coupled cluster reference function.…”

Section: Methodsmentioning

confidence: 99%

Modeling the electronic structures of the ground and excited states of the ytterbium atom and the ytterbium dimer: A modern quantum chemistry perspective

Tecmer

Boguslawski

Borkowski

et al. 2019

Int J of Quantum Chemistry

Self Cite

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“…Results building upon AP1roG/pCCD are quite promising. [159][160][161][162][163][164][165][166][167][168][169]…”

Section: B Ap1rog/pccdmentioning

confidence: 99%

Density Matrices of Seniority-Zero Geminal Wavefunctions

Moisset,

Fecteau,

Johnson

2022

Preprint

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Scalar products and density matrix elements of closed-shell pair geminal wavefunctions are evaluated directly in terms of the pair amplitudes, resulting in an analogue of Wick's theorem for fermions or bosons. This expression is in general intractable, but it is shown how it becomes feasible in three distinct ways for Richardson-Gaudin (RG) states, the antisymmetrized geminal power, and the antisymmetrized product of strongly-orthogonal geminals. Dissociation curves for hydrogen chains are computed with off-shell RG states and the antisymmetrized product of interacting geminals.Both are near exact suggesting that the incorrect results observed with ground state RG states are fixable using a different RG state.

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“…22 Both the pCCD and pCCD-LCC ansätze have been extended to model excited states using the Equation of Motion (EOM) formalism. [23][24][25][26][27] The first version of the code, PyBEST v1.0.0, was released on July 1, 2020, and is available free of charge. 28 Most recent changes are available at the PyBEST project homepage.…”

Section: Introductionmentioning

confidence: 99%