The suitability factor

The suitability of light-atom crystals for charge density analysis can be understood in terms of the relative importance of core electron scattering. As the perturbation of the core electrons by the chemical environment is beyond the reach of practically all experimental studies, the frozen-core approximation is routinely used. It assumes the intensity of the core electron scattering to be invariable, while the valence scattering is affected by the chemical environment, as discussed in chapter 

The value of the suitability factor S varies from typically 3-5 for first-row atom organic crystals to 0.1-0.3 for metals and alloys of first row transition metal elements. (Table 12.1). The implication is that much better accuracy will be 

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