Time-dependent Hartree-Fock theory and long-range interactions

It is shown that time-dependent Hartree-Fock theory can be used to calculate the interaction potential of atomic systems at large separations. Explicit calculations are performed for a pair of helium atoms with the result that at a separation Ra 0 the interaction potential, in atomic units, is given by V ( R ) = -{1.376/ R 6 + 13.18/ R 8 + 169.8/ R 10 + O(1/ R 11 )}. Comparison with other data suggests that the coefficients are too small by about 7% and the interaction potential is accordingly more accurately represented by V ( R ) = -{1.47/ R 6 + 14.1/ R 8 + 182/ R 10 + O(1/ R 11 )}. Calculations of the non-additive long-range interaction potential for three helium atoms are also reported.