Regular approximated scalar relativistic correlated ab initio schemes: applications to rare gas dimers

The ab initio scalar ZORA approach, which was previously tested within the context of numerical and basis set SCF calculations, is generalized to incl ude electron correlation. The technical details of the method are investiga ted in calculations on the systems Ne-2, Ar-2, Kr-2 and Xe-2. For the weakl y bonded rare gas dimers we calculated the bond lengths and well depths usi ng the non-relativistic ZORA and scaled ZORA MP2 method. The relativistic e ffect on the potential energy minimum, obtained with the most accurate meth od (scaled ZORA) is shown to be very close to that of the Dirac-Fock MP2 me thod.