Restraint weight factor

In RESP fit, restraint that keeps the atomic charge near zero are applied to each atom with a uniform weighting factor. In this fitting method, different weighting factors are assigned to the atoms, which are reversely proportional to the square of the base charges. 

A molecular dynamics force field is a convenient compilation of these data (see Chapter 2). The data may be used in a much simplified fonn (e.g., in the case of metric matrix distance geometry, all data are converted into lower and upper bounds on interatomic distances, which all have the same weight). Similar to the use of energy parameters in X-ray crystallography, the parameters need not reflect the dynamic behavior of the molecule. The force constants are chosen to avoid distortions of the molecule when experimental restraints are applied. Thus, the force constants on bond angle and planarity are a factor of 10-100 higher than in standard molecular dynamics force fields. Likewise, a detailed description of electrostatic and van der Waals interactions is not necessary and may not even be beneficial in calculating NMR strucmres. 

Wp is the weight given to the phase restraint, and / is a square well function with a width equal to the arccosine of the figure of merit (fom(h)) for each reflection. Another possible form of Exray which we call the vector residual does not use the amplitude residual at all but instead simultaneously restrains the real (A) and imaginary (B) parts of the structure factor [24]. It has the form... 

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