Local, gradient-corrected, and hybrid density functional calculations on Pd-n clusters for n=1-6

Full optimizations of Pd-n cluster geometries have been performed using density functional methods and allowing the occurrence of low-symmetry structures. To account for at least partially for relativistic effects, use was made of Hay and Wadt RECP. The following ground states were found respectively for n = 1, 2, 3, 4, and 6: S-1(4d(10)), (3) Sigma(u)(+), B-3(2) {C-2v}, B-3(2) {C-2v}, B-3(2g) {D-4h}. Various exchange-correlation functionals have been tested on Pd-2 and Pd-3, including the recent B3LYP one. The introduction of some exact exchange reduces significantly the predicted binding energy, which thus matches the experimental values in the case of Pd-2. Moreover, it allows us to overcome the serious SCF convergence problems arising from the presence in these clusters of a large number of low-lying, nearly degenerate states.