Diagrammatic valence-bond

Z. G. Soos and S. Ramasesha, Diagrammatic valence bond theory, in Valence Bond Theory and Chemieal Structure (D. J. Klein and N. Trinajstic. eds.), Elsevier, Amsterdam. 1990, p. 81. 

The modest a-jt overlap in open-shell molecular solids suggests an approach based on separated molecular fragments Structural and spectroscopic evidence supports the occurrence of essentially unperturbed molecules or molecular ions in the solid state. Since valence-bond (VB) treatments of molecules become exact in the dissociated-atom limit, a diagrammatic VB approach has been developed for open-shell molecular solids. The resulting correlated crystal states are simply weighted linear combinations of VB structures for the entire solid. 

This edition, a completely rewritten and expanded version of the original, includes second quantization and diagrammatic perturbation theory, symmetric and unitary group methods, new forms of valence bond theory, dynamic properties and response, propagator and equation-of-motion techniques and the theory of intermolecular forces. 

To understand what happens to the valence electrons during a reaction mechanism there is a diagrammatic way making use of curly arrows. For example, the above mechanism can be explained by using a curly arrow to show what happens to the lone pair of electrons (Following fig.). In this case, the arrow starts from a lone pair of electrons on the oxygen (the source of the two electrons) and points to where the centre of the new bond will be formed. 

Lewis Electron-Dot Formulas Lewis electron-dot formulas are diagrammatic representations of the atoms involved and their valence electrons. The valence electrons are usually represented as dots around the elemental symbol. It is a two-dimensional way of representing the structuralformula, showing the bonding electrons and the lone electrons that are in the valence shells. 

The change in the band structure arising from the Peierls transition is shown diagrammatically in Figure 1.11 [190]. According to convention in semiconductor physics, the lower (and filled) sub-band is called the valence band the upper (empty) sub-band, the conduction band. In chemistry the terms n and n band are common the former contains the bonding ... 

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