The accuracy of the one-term Gaussian representation for core electrons in calculating the experimental valence charge density of KCl

The scattering factors of the 1s²2s²2p⁶ core for K⁺ and Cl^- have been calculated from analytical wave functions and also with one-term Gaussian representations. These scattering factors, together with the experimental structure factors, have been used to obtain, by difference Fourier inversion, the valence-electron charge distributions of KCl in the [100], [110] and [111] directions. By comparison, a very simple one-term Gaussian representation has been shown to yield reliable results.