Isodensity contours fragments

The fundamental principle we shall follow in the local shape analysis of functional groups and local molecular moieties is a strict analogy with the shape analysis of complete molecules. Accordingly, instead of molecular isodensity contour (MIDCO) surfaces, the main tool of analysis will be the fragment isodensity contour (FIDCO) surfaces. Some of the ideas and concepts described in this section are illustrated in Figure 1. 

Fi e 3 Two approximate isodensity surfaces of the butadiene molecule, obtained for density contour parameter values a = 0.25c/(a.u.) and a = 0.02c/(a.u.), respectively. Note that according to the density domain approach (DDA) to chemical bonding, all molecular fragments are bonded together at both density levels shown. 

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