1,720,996 research outputs found
Accurate computed singlet–triplet energy differences for cobalt systems: implication for two-state reactivity
No full textInternational audienceAccurate singlet-triplet energy differences for cobalt and rhodium complexes were calculated by using several wave function methods, such as MRCISD, CASPT2, CCSD(T) and BCCD(T). The considered systems are built by increasing progressively the first coordination sphere around the metal. We included in our set two CpCoX complexes (Cp = cyclopentadienyl, X = alkenyl ligand), which have been suggested as intermediates in cycloaddition reactions, presenting a two-state reactivity. Most of the considered systems display a triplet ground state. However, in the case of a reaction intermediate, while a triplet ground state was predicted on the basis of Density Functional Theory results, our calculations suggest a singlet ground state. This stems from the competition between the exchange term (stabilising the triplet) and the accessibility of an intramolecular coordination (stabilising the singlet). This finding has an impact on the general mechanism of the cycloaddition reaction. Analogous rhodium systems were also studied
Localized Structures at the Hückel Level, a Hückel-Derived Valence Bond Method
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Hückel-Lewis Projection Method: A “Weights Watcher” for Mesomeric Structures †
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Recasting Wave Functions into Valence Bond Structures: A Simple Projection Method to Describe Excited States
No full textInternational audienceA 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 cat-ion, 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.
Experimental studies of collisions of excited Li(4p) atoms with C2H4, C2H6, C3H8 and theoretical interpretation of the Li–C2H4 system
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Multidimensional Isotropic Magnetic Shielding Contour Maps for the Visualization of Aromaticity in ortho-Arynes and Their Reactions
No full textAbstract Visualization of electron delocalization and aromaticity in some selected arynes, including nonplanar examples, and their Diels–Alder or dimerization reactions was achieved through multidimensional isotropic magnetic shielding contour maps. These maps showed that arynes are generally less aromatic than the corresponding arenes, and that aromaticity peaks during their reactions when approaching the transition state
HuLiS a program to recast molecular orbital wave functions into Lewis structures
No full textInternational audienceThe HuLiS program is presented as a tool to decompose a delocalized wave function as a linear combination of localized electronic structures. The principles of the energy based HL-CI and the overlap based schemes HL-P are developed. The results obtained for a set of 10 relevant organic molecules are shown to compare very well with high level quantum chemistry calculations. A trust factort is introduced and its use is shown on the allyl radical case where symmetry must be taken into account
Hückel theory for Lewis structures: Hückel–Lewis Configuration Interaction (HL-CI)
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