A COMPARATIVE-STUDY ON THE STRUCTURE OF M2SE AND M2I+ (M=AG, AU) USING PSEUDOPOTENTIALS AND FULL AB-INITIO METHODS

The molecules of M2Se and M2I+ (M = Ag, Au) are used as test models to study the quality of the pseudopotential methodology when using the Hartree-Fock and second-order Moller-Plesset methods. We have used two implementations of the Wadt and Hay pseudopotentials: the new large- and small-core pseudopotentials (known as LANL1DZ and LANL2DZ in GAUSSIAN-92) and the traditional one used for a long time. It is found that the optimum geometry depends on the type of pseudopotential selected. A comparison with the results computed when all the electrons are taken explicitly into accounts shows that the new LANL1DZ and LANL2DZ give the right answer. Using these potentials, the geometry and potential energy surface of the M2Se and M2I+ systems is explored and its optimum geometry found. (C) 1994 John Wiley & Sons, Inc.