Configuration interaction and Hylleraas configuration interaction methods in valence bond theory. Diatomic two‐electron systems

1991 ◽  
Vol 95 (4) ◽  
pp. 2572-2576 ◽  
Author(s):  
Wojciech Cencek ◽  
Jacek Komasa ◽  
Jacek Rychlewski
Keyword(s):  
Configuration Interaction ◽  
Valence Bond ◽  
Electron Systems ◽  
Valence Bond Theory ◽  
Bond Theory

Electronic levels in simple conjugated systems, I. Configuration interaction in cyclobutadiene

1950 ◽  
Vol 202 (1071) ◽  
pp. 498-506 ◽  
Keyword(s):  
Molecular Orbital ◽  
Configuration Interaction ◽  
Energy Levels ◽  
Valence Bond ◽  
Wave Functions ◽  
The Other ◽  
Orbital Theory ◽  
Valence Bond Theory ◽  
Symmetry Properties ◽  
Bond Theory

In the simplest cyclic system of π-electrons, cyclobutadiene, a non-empirical calculation has been made of the effects of configuration interaction within a complete basis of antisymmetric molecular orbital configurations. The molecular orbitals are made up from atomic wave functions and all the interelectron repulsion integrals which arise are included, although those of them which are three- and four-centre integrals are only known approximately. In this system configuration interaction is a large effect with a strongly differential action between states of different symmetry properties. Thus the 1 A 1g state is several electron-volts lower than the lowest configuration of that symmetry, whereas for 1 B 1g the comparable figure is about one-tenth of an electron-volt. The other two states examined, 1 B 2g and 3 A 2g are affected by intermediate amounts. The result is a drastic change in the energy-level scheme compared with that based on configuration wave functions. Neither the valence-bond theory nor the molecular orbital theory (in which the four states have the same energy) gives a satisfactory account of the energy levels according to these results. One conclusion from the valence-bond theory which is, however, confirmed, is the somewhat unexpected one that the non-totally symmetrical 1 B 2g state is more stable than the totally symmetrical 1 A 1g . On the other hand, it is clear that the valence-bond theory, with the usual value for its exchange integral, grossly exaggerates the resonance splitting of the states, giving separations between them several times too great. Thus the valence-bond theory leads to large values of the resonance energy (larger, per π-electron, than in benzene) and so associates with the molecule a considerable π-electron stabilization. This expectation has no support in the present more detailed and non-empirical calculations.

The Atomic Exciton Model for the Excited States of p-Electron Systems

1985 ◽  
Vol 38 (10) ◽  
pp. 1529
Author(s):  
PE Schipper
Keyword(s):  
Excited States ◽  
Ground State ◽  
Valence Bond ◽  
Essential Difference ◽  
Electron Systems ◽  
Exciton Model ◽  
Valence Bond Theory ◽  
Bond Theory ◽  
Atomic Excitations ◽  
Insight Into

A new model is presented to describe the π-π* excitations of π-electron systems in terms of intra-atomic excitations. The atomic exciton model combines features of conventional exciton and valence bond theory, reducing to the former in the non-exchanging limit, and the latter in the ground-state limit with covalent structures. The model is ideally suited to the approximate or exact incorporation of exchange, and highlights the opposition of excitation and electron interchange in determining the energetics of the excitation manifold, eliciting thereby the essential difference between ground and excited states. Applications to some simple π-systems are considered, providing new insight into their excited states.

scholarly journals The electronic structure of carbones revealed: insights from valence bond theory

2021 ◽  
Vol 23 (5) ◽  
pp. 3327-3334
Author(s):  
Remco W. A. Havenith ◽  
Ana V. Cunha ◽  
Johannes E. M. N. Klein ◽  
Francesca Perolari ◽  
Xintao Feng
Keyword(s):  
Electronic Structure ◽  
Valence Bond ◽  
Carbon Suboxide ◽  
Valence Bond Theory ◽  
Bond Theory

Valence bond theory reveals the nature of the OC–C bond in carbon suboxide and related allene compounds.

ChemInform Abstract: Study of the Electronic States of the Benzene Molecule Using Spin- Coupled Valence Bond Theory.

ChemInform ◽  
2010 ◽  
Vol 26 (7) ◽  
pp. no-no
Author(s):  
E. C. DA SILVA ◽  
J. GERRATT ◽  
D. L. COOPER ◽  
M. RAIMONDI
Keyword(s):  
Valence Bond ◽  
Electronic States ◽  
Benzene Molecule ◽  
Valence Bond Theory ◽  
Bond Theory
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