Theory of the d(10)-d(10) closed-shell attraction .1. Dimers near equilibrium

We study the dependence of the aurophilic attraction (Au-1-Au-1) in perpendicular model systems of the type [(ClAuPH3)(2)] on the ab initio method, basis set and different pseudopotentials used, and on relativity. The effects of varying the ''halogen'' (X = F, H, Cl, Me, Br, -C=CH, I), the ''phosphine'' (L = PH3, PMe3-N=CH) and the metal (M = Cu, Ag, Au) on the M-M' interaction of the [(XML)(2)] dimer are also studied. The depth of the interaction potential increases with the softness of the group X. It decreases by 27% for M = Au, X = Cl and L = PH3 if relativistic effects are omitted at fixed geometry.