DESCRIBING VAN-DER-WAALS INTERACTION IN DIATOMIC-MOLECULES WITH GENERALIZED GRADIENT APPROXIMATIONS - THE ROLE OF THE EXCHANGE FUNCTIONAL

Generalized gradient approximations have been used to calculate the po tential energy curves for six rare gas diatomic molecules. Several gen eralized gradient approximations are found to provide a good descripti on of binding in these diatomic molecules and show a significant impro vement over the local density approximation in the prediction of bond lengths and dissociation energies. It is shown here that the behavior of an exchange functional in the region of small density and large den sity gradient plays a very important role in the ability of the functi onal to describe this type of van der Waals attraction. (C) 1997 Ameri can Institute of Physics.