Electron density: an exponential model

Electron density ideally is positive definite. The imperfect experimental data of an X-ray diffraction experiment do not lead to such a function when the density is obtained from structure factors by the linear relationship of Fourier transformation. At the price of certain but quite small bias, electron density may be represented by an otherwise completely general exponential model. The model is based on iterative correction of a logarithm which yields a density approximation of resolution substantially higher than that afforded by Fourier transformation of structure factors.