Electronic reorganization errors

In this respect, the CNDO and INDO methods have met with very little success, the values usually being too high by 3.5 eV to 5 eV. The error here seems too large even if provision is made for the possible reorganization of electrons in the molecule. 

The difference Ag(X) = p(X) - Pm(X) between the actual density and the pro-molecule density is known as the deformation density and can be interpreted as the electron density reorganization that occurs when a collection of independent, isolated, spherically symmetric atoms is combined to form a molecule in a crystal. Since Aq is only a very small fraction of total Q in the region of the atoms, it is very susceptible to experimental error in the X-ray measurements and to inadequacies in the model, namely errors in the assumed atomic positions, atomic scattering factors, and ADPs. In one approximation, a deformation density map is obtained by direct subtraction of the two densities. The density map obtained in this way is smeared by vibrational motion of the atoms, but its peaks and troughs can often be interpreted in terms of some model of chemical bonding, e.g., peaks between bonded atoms being identified with bonding density and so on. A difference density map for tetrafluoroterephthalodinitrile [27] is shown in Fig. 3. 

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