The maximum entropy method in accurate charge-density studies

The maximum entropy method (MEM) can be used to determine the electron density in the unit cell from phased x-ray diffraction data. A critical discussion is given of the possibilities and limitations of the MEM for the determination of accurate electron densities in chemical bonds. An overview is given of the principles of the MEM, and recent extensions and modifications are discussed, as they are required for a successful application of the MEM in accurate charge-density studies. The quantitative interpretation of MEM electron densities according to Bader's atoms-in-molecules (AIM) theory is discussed, and it is compared to AIM properties of densities obtained from multipole refinements. Applications are presented concerning the analysis of covalent bonds and hydrogen bonds in molecular crystals.