GRADIENT CORRECTIONS IN DENSITY-FUNCTIONAL THEORY CALCULATIONS FOR SURFACES - CO ON PD(110)

Ab initio total energy calculations have been performed for CO chemiso rption on Pd(110). Local density approximation (LDA) calculations yiel d chemisorption energies which are significantly higher than experimen tal values but inclusion of the generalised gradient approximation (GG A) gives better agreement. In general, sites with higher coordination of the adsorbate to surface atoms lead to a larger degree of overbindi ng with LDA, and give larger corrections with GGA. The reason is discu ssed using a first-order perturbation approximation. It is concluded t hat this may be a general failure of LDA for chemisorption energy calc ulations. This conclusion may be extended to many surface calculations , such as potential energy surfaces for diffusion.