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

Abstract

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

A systematic approach to vertically excited states of ethylene using configuration interaction and coupled cluster techniques

“…The EOM-CCSDT excitation energy in the same basis set was reported to be 7.89 eV. The authors concluded that nonadiabatic effects were important in shifting the vertical excitation energy to higher energy than the experimental observed band maximum, in disagreement with the findings of Müller et al 52 In 2014 Wu et al 70 used the valence bond self consistent field (VBSCF) and breathing orbital valence bond (BOVB) methods with several basis sets. V state T v values ranged from 9.…”

Surface Hopping Dynamics with DFT Excited States

“…Ethylene S 1 surface is a specially challenging problem, starting from (i) the adequate computation of the excitation into the V state [6], then (ii) the description of the right topography of the state, which includes a crossing with the Z state near the twisted structure and a conical intersection at twisted-pyramidalized geometries Surface Hopping Dynamics with DFT Excited States [115], to finally (iii) the dynamics evolution itself, which has motivated a long debate between theorists and experimentalists [117][118][119]. In fact, Levine et al [120] have used maps similar to those in Fig.…”

“…Not only are such values of the order of magnitude of many reaction barriers, but also these errors are unevenly distributed among several states for the same method and tend to grow bigger out of the Franck-Condon region. Well known examples are the relatively large errors of the energy of ionic states predicted by truncated ab initio configuration interaction [6] or of the energy of charge-transfer states of time-dependent density functional theory with conventional functionals [7].…”

Recasting wave functions into valence bond structures: A simple projection method to describe excited states

“…The allyl cases are possibly simple cases, but they give the opportunity to test how symmetry is accounted for while no constraint is provided. The ethene case is a reputedly difficult case from the MO point of view, and was recently considered at the VB level …”

“…The literature on ethene's excited states, and particularly on the V state (1 1 B 1u ), is very rich, and the recent paper published last year by Feller et al provides a detailed survey of the subject, particularly in their Supporting Information. To put it in a nutshell, the ground state (1 1 A g ) is called the N state, and the 1 B 1u excited state is called the V state . The V state is reputedly difficult to describe due to some mixing with a Rydberg state of same symmetry (2 1 B 1u ), and the starting orbitals are of great importance.…”