INTERMOLECULAR INTERACTIONS OF DICHLOROMETHANE WITH PD(IV) ORGANOMETALLIC COMPOUNDS - CAN WE USE SMALL BASIS-SETS IN AB-INITIO MP2 AND DFT CALCULATIONS

The interaction of CH2Cl2 with the different ligands of PdCl(H)(3)(NH3 )(2) is studied, showing the effect of the level of the method used, t ogether with that of the basis sets employed in ab initio calculations . The position of the minimum, generally determined without BSSE corre ction by the gradient geometry optimization method in supermolecule tr eatment, has been systematically reoptimized pointwise with a counterp oise BSSE correction. It is seen that the change of the minimum is muc h larger with MP2, than with DFT calculations, The DFT geometry obtain ed without BSSE correction is close to the BSSE-corrected MP2 one. How ever, the BSSE-corrected DFT and MP2 interaction energies may differ b y as much as 50%, the MP2 energies being in good agreement with MP4(SD TQ) results. The strategy of a low-cost DFT(B3LYP) optimization of the geometry followed by the computation of the BSSE-corrected MP2 energi es appears to be reliable in this type of investigation. (C) 1998 Else vier Science B.V.