SIMPLE TESTS FOR DENSITY-FUNCTIONAL METHODS

The performance of the currently used generalized gradient approximati on density functionals is analyzed using several simple, yet critical requirements. We analyze the effects of the self-interaction error, th e inclusion of the exact exchange, and the parameter settings used in the popular three-parameter hybrid density functionals. The results sh ow that the elimination of the self-interaction error from the current density functionals lead to very poor results for H-2. The inclusion of the exact exchange does not significantly influence the self-intera ction corrected results. The variation of the A, B, and C parameters o f a hybrid DFT method influences the H-H equilibrium bond length throu gh a very simple Linear equation, and it is possible to reproduce the experimental H-H distance with appropriate selection of these paramete rs, although an infinite number of solutions exists. Similar results w ere obtained for the total energy and the electron density along the i nternuclear axis. The analysis of the exact KS potential at the bond c ritical point of the dissociating H-2 molecule shows that, for this pr operty, the second order Moller-Plesset perturbation theory yields a b etter potential than the density functionals studied in this article. (C) 1997 John Wiley & Sons, Inc.