Bonding without ionisation

Charges are calculated for diatomic molecules by partitioning the promolecu lar density with projection operators derived from free atom potentials. Th e promolecular charges thus obtained have physically reasonable magnitudes, which are moderately sensitive to interatomic distances and thus to bond t ype. Their signs are negative for cations and positive for anions. Trends i n these charges correlate with subshell structure. Due to the long range of their electrostatic potentials, the cations compete successfully for elect rons at the expense of the anions in the density partitioning. This implies that the cation states become overfilled when the atoms overlap, favouring a flow of electrons away from the cation towards the vacant anion states. That accounts for the positive cations and negative anions observed when mo lecular densities are partitioned with projection operators based on free a tom electron densities.