Modelling electrostatic potential from experimentally determined charge densities. I. Spherical-atom approximation

Observations of the experimental electrostatic potential obtained from X − X spherical electron density can be used to derive point charges centred on the atoms. This is applied to a pseudopeptide, N-acetyl-α, β-dehydrophenylalanine methylamide. The experimentally determined charges are consistent whatever the sampling points and `follow' the atomic site when the conformation of the molecule changes. However, introduction of multipolar moments is necessary as soon as the aspherical part of the electron density is added.