The interaction of a water molecule with an ion at a distance

The interaction of an ion with a water molecule at intermediate separation is considered. It is shown that the SCF interaction energy in the small overlap region can be calculated as the sum of the electrostatic and induction terms. For the electrostatic interaction multipoles up to hexadecapoles must be included. The induction term, which is appreciable, may be accurately obtained from the α, A, and C tensors.