A generalized Brillouin theorem (GBT)-like implementation to optimize Valence Bond wave function for excited states

Racine, Julien; Carissan, Yannick; Hagebaum‐Reignier, Denis; Humbel, Stéphane

doi:10.1016/j.comptc.2017.01.019

Cited by 2 publications

(1 citation statement)

References 41 publications

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“…For more than two decades, the BOVB method has been applied to many ground-state properties and was shown to provide accurate bonding energies and reaction barriers . By contrast, it has almost never been applied to excited states, with the exception of the “ionic” V state of ethylene, , a calculation facilitated by the fact that this state, though quite challenging, is the lowest one in its symmetry (see below and in the Appendix). On the other hand, it could not be applied, up to now, to the vast category of excited states that have the same symmetry as the ground state, or are not the lowest states in their symmetry group, for lack of an SA version of ab initio VB methods.…”

Section: Introductionmentioning

confidence: 99%

Valence Bond Alternative Yielding Compact and Accurate Wave Functions for Challenging Excited States. Application to Ozone and Sulfur Dioxide

Braı̈da

Chen

et al. 2020

J. Chem. Theory Comput.

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A novel state-averaged version of ab initio nonorthogonal valence bond method is described, for the sake of accurate theoretical studies of excited states in the valence bond framework. With respect to standard calculations in the molecular orbital framework, the state-averaged breathingorbital valence bond (BOVB) method has the advantage to be free from the penalizing constraint for the ground and excited state(s) to share the same unique set of orbitals. The ability of the BOVB method to faithfully describe excited states and to compute accurate transition energies from the ground state is tested on the five lowest-lying singlet electronic states of ozone and sulfur dioxide, among which 1 1 B 2 and 2 1 A 1 are the challenging ones. As the 1 1 A 2 , 1 1 B 1 , and 1 1 B 2 states are of different symmetries than the ground state, they can be calculated at the state-specific BOVB level. On the other hand, the 2 1 A 1 states and the 1 1 A 1 ground states, which are of like symmetry, are calculated with the state-averaged BOVB technique. In all cases, the calculated vertical energies are close to the experimental values when available, and at par with the most sophisticated calculations in the molecular framework, despite the extreme compactness of the BOVB wave functions, made of no more than 5−9 valence bond structures in all cases. The features that allow the combination of compactness and accuracy in challenging cases are analyzed. For the "ionic" 1 1 B 2 states, which are the site of important charge fluctuations, it is because of the built-in dynamic correlation inherent to the BOVB method. For the 2 1 A 1 ones, this is the fact that these states have the degree of freedom of having different orbitals than the ground states, even though they are of like symmetry and calculated simultaneously using the newly implemented state-average BOVB algorithm. Finally, the description of the excited states in terms of Lewis structures is insightful, rationalizing the fast ring closure for the 2 1 A 1 state of ozone and predicting some diradical character in the socalled "ionic" 1 1 B 2 states.

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Section: Introductionmentioning

confidence: 99%

Valence Bond Alternative Yielding Compact and Accurate Wave Functions for Challenging Excited States. Application to Ozone and Sulfur Dioxide

Braı̈da

Chen

et al. 2020

J. Chem. Theory Comput.

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Taming the excited states of butadiene, hexatriene, and octatetraene using state specific multireference perturbation theory with density functional theory orbitals

Manna

Chaudhuri

Chattopadhyay

2020

The Journal of Chemical Physics

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To compute the electronic excitation energies, a state-specific multireference Møller–Plesset perturbation theory (SSMRPT) with a complete active space configuration interaction reference function constructed using the orbitals obtained by the density functional theory (DFT) is presented as an accurate, as well as computationally affordable, and efficient protocol at the level of second order. The global hybrid B3LYP (Becke, 3-parameter, Lee–Yang–Parr) functional has been used to generate orbitals. The present method, called DFT-SSMRPT, uses perturbers that are individual Slater determinants and accounts for the coupling between the nondynamical and dynamical correlation effects. We have applied the new method to compute excitation energies in conjugated systems of π-electrons such as trans-1,3-butadiene, trans,trans-1,3,5-hexatriene, and all-trans-1,3,5,7-octatetraene. The ordering of the excited states is correctly reproduced by the DFT-SSMRPT calculations. The relative ordering of low-lying excited 1Bu and 1Ag states alters when the length of the polyene changes. The results match reasonably well with the literature including experimental and best theoretical findings. The accuracy of the method is sufficient to discern the energy gap between the close low-lying singlet and triplet states. The DFT-SSMRPT appears as an affordable computational ab initio avenue for a qualitatively correct description of excitation energies.

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A generalized Brillouin theorem (GBT)-like implementation to optimize Valence Bond wave function for excited states

Abstract: International audienc

Cited by 2 publications

References 41 publications

Valence Bond Alternative Yielding Compact and Accurate Wave Functions for Challenging Excited States. Application to Ozone and Sulfur Dioxide

Valence Bond Alternative Yielding Compact and Accurate Wave Functions for Challenging Excited States. Application to Ozone and Sulfur Dioxide

Taming the excited states of butadiene, hexatriene, and octatetraene using state specific multireference perturbation theory with density functional theory orbitals

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