title: Recasting wave functions into valence bond structures: A simple projection method to describe excited states.
abstract: A method is proposed to obtain coefficients and weights of valence bond (VB) determinants from multi configurational wave functions. This reading of the wave functions can apply to ground states as well as excited states. The method is based on projection operators. Both energetic and overlap-based criteria are used to assess the quality of the resulting VB wave function. The approach gives a simple access to a VB rewriting for low-lying states, and it is applied to the allyl cation, to the allyl radical and to the ethene (notably to the V-state). For these states, large overlap between VB and multi reference wave functions are easily obtained. The approach proves to be useful to propose an interpretation of the nature of the V-state of ethene.
authors.affiliation: Aix Marseille Université, CNRS, Centrale Marseille, iSm2 UMR 7313, Marseille, 13397, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Racine
authors.affiliation: Aix Marseille Université, CNRS, Centrale Marseille, iSm2 UMR 7313, Marseille, 13397, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Hagebaum-Reignier
authors.affiliation: Aix Marseille Université, CNRS, Centrale Marseille, iSm2 UMR 7313, Marseille, 13397, France.
authors.forename: Yannick
authors.initials: Y
authors.lastname: Carissan
authors.affiliation: Aix Marseille Université, CNRS, Centrale Marseille, iSm2 UMR 7313, Marseille, 13397, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Humbel
keywords: bond theory; electronic structure; excited states; multi reference; valence bond