Charge transfer and dipole moments of polyatomic systems

Heteronuclear molecules have electric dipole moments because of electronic charge transfer among the constituent atoms. Quantum mechanical calculations reproduce the values of observed dipoles quite well, but easy-to-use model theories have so far failed to produce dipole moments in agreement with experiment. By combining density-functional theory and classical concepts, we obtain a simple predictive model for charge transfer which overcomes the shortcomings of earlier models based on the concept of electronegativity equalization. It yields dipole moments for many diatomic molecules and for the water molecule that are in satisfactory agreement with experiment. The model has promise as a supplement of classical molecular dynamics simulations for multicomponent polyatomic systems.