BASIS-INDEPENDENT POTENTIAL-ENERGY CURVES FOR THE NEUTRAL DIATOMICS OF LI, NA AND K EVALUATED BY MEANS OF HARTREE-FOCK AND DIFFERENT DENSITY-FUNCTIONAL POTENTIALS

The solution of the Schrodinger equation for diatomic molecules when t he finite element method is used gives the possibility to evaluate hig hly accurate basis-independent potential energy curves. In this work s uch types of numerically accurate potential energy curves on the HF le vel have been evaluated for Li2, Na2 and K2 and could be used as bench marks in the optimization of basis sets. A comparison between recent L CAO HF calculations in which extended basis sets are used and the accu rate values determined in this work show that there is a difference in total energy of 4 x 10(-5) and 10(-3) a.u. for Li, Li2, and Na, Na2, respectively. Evaluated dissociation energies are, however, due to the cancellation of numerical errors in much better agreement. Further, i t is found that different exchange correlation potentials for the heav ier molecules such as those given by von Barth-Hedin and Vosko, Wilk a nd Nusair reproduce experimental properties such as dissociation energ ies, vibrational frequencies almost as well as those achieved with adv anced CI methods. The Xalpha potential gives accurate bond lengths for Na2 and K2, whereas the dissociation energies are too small.