In theoretical chemistry and molecular physics, Coulson–Fischer theory provides a quantum mechanical description of the electronic structure of molecules.
[3] Modern valence bond theory is often seen as an extension of the Coulson–Fischer method.
This is described for H2 as follows:[1] where a and b are atomic 1s orbitals, that are used as the basis functions for VBT, and λ is a delocalization parameter from 0 to 1.
[5] However, an expansion of the Coulson-Fischer description of the wavefunction in terms of a and b gives: A full VBT description of H2 that includes both ionic and covalent contributions is where ε and μ are constants between 0 and 1.
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