Determination of the atomic charge on sodium in sodium salts by numerical integration — a theoretical investigation

The electron density difference in a NaSCN crystal is set up from the ab initio densities of Na⁺ and SCN^? ions and compared to the experimental counterpart based on X-ray diffraction measurements. Numerical integration over the electron density difference is executed around the Na⁺ ion. The atomic charge (+0.20e) derived in this way is in good agreement with the analogous experimental charge (+0.27e) The low experimental value cannot therefore be taken as an indication for a predominantly non-ionic structure of NaSCN and similar sodium salts