Covalent promolecule

As an illustration (see Scheme 1.2a), let us again consider the two-AO channel of Scheme 1.1a. We first observe that the input-dependent distributions in this model are identical with the molecular distribution (see Eq. [18]). The partial and average IT descriptors are also reported in this diagram, relative to the reference distribution p° = (1 /2,1 /2) of the covalent promolecule, when two AOs contribute a single electron each to form the chemical bond. 

In early experimental studies predominantly in the 1970s and 1980s, so-called deformation electron density studies were typically conducted. Thus, the electron density is modeled using the approach described above, and the electron density of a promolecule (procrystal), constructed by placing spherical free atoms densities at all atomic centers, is subtracted from the fully modeled density. The difference then shows the redistribution of electron density that arises due to chemical bond formation. This approach readily shows electron density buildup in the center of most covalent... 

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