Multireference configuration interaction study of the mixed Valence–Rydberg character of the C2H4 (π,π*)1V state

Krebs, Stefan; Buenker, Robert J.

doi:10.1063/1.473275

Cited by 31 publications

(36 citation statements)

References 24 publications

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“…Further calculations have confirmed this consideration and the effect due to these excitations is called dynamic σ polarization and it is part of what is called dynamic σ -π correlation. As in the case of the vertical excitation energy, the best values 11,13 for x 2 have been obtained by a heavy computational effort, employing the highest level ab initio methods, and carefully controlling the computational parameters (in particular the nature of the orbitals used in the CI expansion), because a relatively slow convergence has been observed.…”

Section: Introductionmentioning

confidence: 99%

On the nature of the π → π* ionic excited states: The V state of ethene as a prototype

2008

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This article addresses an analysis of the physical effects required for the correct description of the ionic pi --> pi* excited states in the frame of ab initio quantum chemistry, using the ionic V state of the ethene molecule as an example. The importance of the dynamic sigma polarization (absent in methods where the sigma skeleton is treated at a mean-field level) has been recognized by many authors in the past. In this article a new physical effect is described, i.e. the spatial contraction of the pi and pi* molecular orbitals (or of the local p atomic orbitals) originated from the reduction of the ionicity due to the dynamic sigma polarization. Such an effect is a second-order effect (it appears only as a consequence of the dynamic sigma polarization) but it cannot be ignored. Many of the difficulties found in the past in the calculation of the vertical excitation energy of the ionic states are attributed to an incomplete description of this contraction, while the few successes have been obtained when it has been fortuitously introduced by ad hoc procedures or when it is described in a brute force approach. Various strategies are proposed to allow for the spatial contraction of the p atomic orbitals. If this effect is considered at the orbital optimization step, it is shown that for the V state of ethene no Rydberg/valence mixing occurs and a simple perturbation correction (to the second order in the energy) on the pi --> pi* singly excited configuration gives stable results with respect to the computational parameters and in good agreement with the experimental findings and with the best theoretical calculations. Moreover, our results confirm the indication of Müller et al. (J Chem Phys 1999, 110, 7176) that the transition to the V state of ethene conforms to the Franck-Condon principle and that it is not necessary to appeal to a nonvertical transition to interpret the experimental data. The strategy reported in this article for ethene can be in principle generalized to the pi --> pi* ionic excited states of other molecules.

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Section: Introductionmentioning

confidence: 99%

On the nature of the π → π* ionic excited states: The V state of ethene as a prototype

2008

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“…p * excitation of a C-C double bond is one of the most fundamental processes in photochemistry and the ethene molecule, which is the smallest hydrocarbon with a C-C double bond, has thus attracted much research, both on its electronic structure [1][2][3][4][5][6][7][8] and on its dynamics [9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Photoinduced nonadiabatic dynamics of ethene: Six-dimensional wave packet propagations using two different approximations of the kinetic energy operator

et al. 2007

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“…Krebs and Buenker performed an MRCI calculation in large basis set, including up to more than one million configurations state functions (CSFs), and estimated T e in the range 7.90-7.95 eV [29]. An even more extensive MRCI calculation was performed by Müller et al [30], including up to 80 million CSFs, yielding a T e value of 7.7 eV.…”

Section: Introductionmentioning

confidence: 99%

The V state of ethylene: valence bond theory takes up the challenge

Zhang

Braı̈da

et al. 2014

Theor Chem Acc

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HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. Further improvement to 7.96/7.93 eV is achieved at the variational and diffusion Monte Carlo (MC) levels, respectively, VMC/DMC, using a Jastrow factor coupled with the same compact VB wave function. Furthermore, the measure of the spatial extension of the V state wave function, 19.14 a 0 2 , is in the range of accepted values obtained by large-scale state-of-the-art molecular orbitalbased methods. The r response to the fluctuations of the p electrons in the V state, known to be a crucial feature of the V state, is taken into account using the breathing orbital valence bond method, which allows the VB structures to have different sets of orbitals. Further valence bond calculations in a larger space of configurations, involving explicit participation of the r response, with 9 VB structures for the N state and 14 for the V state, confirm the results of the minimal structure set, yielding an N ? V transition energy of 7.97 eV and a spatial extension of 19.16 a 0 2 for the V state. Both types of valence bond calculations show that the V state of ethylene is not fully ionic as usually assumed, but involving also a symmetryadapted combination of VB structures each with asymmetric covalent p bonds. The latter VB structures have cumulated weights of 18-26 % and stabilize the V state by about 0.9 eV. It is further shown that these latter VB structures, rather than the commonly considered zwitterionic ones, are the ones responsible for the spatial extension of the V state, known to be ca. 50 % larger than the V state.Keywords Valence bond Á Quantum Monte Carlo Á V state of ethylene Á Breathing orbitals 1 Introduction

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Multireference configuration interaction study of the mixed Valence–Rydberg character of the C2H4 (π,π*)1V state

Cited by 31 publications

References 24 publications

On the nature of the π → π* ionic excited states: The V state of ethene as a prototype

On the nature of the π → π* ionic excited states: The V state of ethene as a prototype

Photoinduced nonadiabatic dynamics of ethene: Six-dimensional wave packet propagations using two different approximations of the kinetic energy operator

The V state of ethylene: valence bond theory takes up the challenge

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