On the treatment of long-range interactions in global potential energy surfaces for chemically bound systems

The convergence of undamped, inverse power series asymptotic van der Waals expansions for the hydrogen molecule is tested. The role of this kind of expansion in the description of global potential energy surfaces for strongly bound molecules is discussed. The single-bond breaking dissociation channel of the water molecule is shown to display the same behaviour. It is suggested that such expansions do not provide a good starting point for this problem as they only become reliable when the interaction energy is very small.