A theoretical study of the diffuseness of the V(1B1u) state of planar ethylene

Lindh, Roland; Roos, Björn O.

doi:10.1002/qua.560350617

Cited by 91 publications

(76 citation statements)

References 36 publications

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“…68 As can be seen in Table V, MS-RASPT2 transition energies for ethene are in agreement with accurate multi-reference CI theoretical studies. [36][37][38] The vertical energy for the lowest 1 B 1u state is computed to be 8.07 eV which is consistent with previous results. 36-38, 40, 50, 51, 58 For the triplet 1 3 B 1u state, the MS-RASPT2 vertical transition energy is found at 4.51 eV, falling in the region of the experimental data.…”

Section: B Excitation Energiessupporting

confidence: 90%

“…Some accurate theoretical studies have led to a final estimate of about 8.0 eV for the vertical transition of the ethene V state. [36][37][38] At the ground state geometry, the V state has a mixed valence-Rydberg character which strongly depends on the level of theory used to describe it.…”

Section: Computation Of Potential Energy Curves For Stretched Etmentioning

confidence: 99%

“…Experimentally, the triplet is found 58 As mentioned above, the position of the excited valence singlet is not well determined experimentally because of the strong mixing with the nearby Rydberg levels, but the value found here is in excellent agreement with other theoretical calculations. [36][37][38] …”

Section: Computation Of Potential Energy Curves For Stretched Etmentioning

confidence: 99%

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A distance-dependent parameterization of the extended Hubbard model for conjugated and aromatic hydrocarbons derived from stretched ethene

Schmalz

Serrano‐Andrés

Sauri

et al. 2011

The Journal of Chemical Physics

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The Hubbard model, which is widely used in physics but is mostly unfamiliar to chemists, provides an attractive yet simple model for chemistry beyond the self consistent field molecular orbital approximation. The Hubbard model adds an effective electron-electron repulsion when two electrons occupy the same atomic orbital to the familiar Hückel Hamiltonian. Thus it breaks the degeneracy between excited singlet and triplet states and allows an explicit treatment of electron correlation. We show how to evaluate the parameters of the model from high-level ab initio calculations on twoatom fragments and then to transfer the parameters to large molecules and polymers where accurate ab initio calculations are difficult or impossible. The recently developed MS-RASPT2 method is used to generate accurate potential energy curves for ethene as a function of carbon-carbon bond length, which are used to parameterize the model for conjugated hydrocarbons. Test applications to several conjugated/aromatic molecules show that even though the model is very simple, it is capable of reasonably accurate predictions for bond lengths, and predicts molecular excitation energies in reasonable agreement with those from the MS-RASPT2 method.

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Section: B Excitation Energiessupporting

confidence: 90%

Section: Computation Of Potential Energy Curves For Stretched Etmentioning

confidence: 99%

Section: Computation Of Potential Energy Curves For Stretched Etmentioning

confidence: 99%

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A distance-dependent parameterization of the extended Hubbard model for conjugated and aromatic hydrocarbons derived from stretched ethene

Schmalz

Serrano‐Andrés

Sauri

et al. 2011

The Journal of Chemical Physics

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“…This last result, which is off by ca. 0.6 eV relative to experiment, as well as the hx 2 i diffuseness value which is found too small for the V state, indicates that basis sets devoid of diffuse basis functions are inappropriate for the problem at hand, as already discovered long ago by Roos et al [59,60]. In accord, the rest of the study will be performed in a triple-zeta basis set augmented with diffuse basis functions on the carbon atoms, and a double-zeta basis set on the hydrogen atoms, so-called aug-VTZ (see Theoretical methods).…”

Section: Vb Calculations In the (2 2) Spacementioning

confidence: 89%

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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“…6 As a consequence this transition is supposed to show a nonvertical behavior. Starting from the experimental data, the "experimental vertical excitation energy" can be obtained following different approaches [6][7][8][9][10] and it has been estimated to be in the range 7.8 6 -8.0 10 eV. On the other hand Müller et al argued in a recent article 11 that "it is not necessary to refer to nonadiabatic effect in order to achieve agreement with the experiments data".…”

Section: Introductionmentioning

confidence: 96%

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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A theoretical study of the diffuseness of the V(¹B_1u) state of planar ethylene

Cited by 91 publications

References 36 publications

A distance-dependent parameterization of the extended Hubbard model for conjugated and aromatic hydrocarbons derived from stretched ethene

A distance-dependent parameterization of the extended Hubbard model for conjugated and aromatic hydrocarbons derived from stretched ethene

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

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

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