Molecular interactions by the time-dependent Hartree method

Abstract

The time-dependent Hartree method gives a new approximate way to calculate dispersion forces between atoms or molecules. We prove that the energy depends on the electrical polarizability of the interacting atoms, which is the same as if the bound ‘dispersion electrons’ in each atom were replaced by an equivalent assembly of harmonic oscillators. The dispersion energy is equal to the change of zero-point energy of the oscillators when the atoms approach. The method gives a simple description of non-additive three-body forces, forces between molecules of large size compared with their separation, and retardation effects at very long distances. The interaction free energy of two systems at any temperature is proved to be equal to the change of free energy of the equivalent oscillators.