AB-INITIO CALCULATION OF MOLECULE-SURFACE BINDING - METHYL HALIDES ONGAAS(110) SURFACES

Large scale ab initio cluster calculations are used to examine the bin ding of methyl halides to the (110) surface of GaAs. The results of th e calculations are compared with recent experimental measurements of t he binding energies. Three approaches to electron correlation are exam ined: density functional methods utilizing the generalized gradient ap proximations (specifically, the BLYP functional) or adiabatic connecti on formulas (B3LYP), and local MP2 methods which intrinsically elimina te basis set superposition errors. The BLYP calculations are found to underestimate the binding substantially; the B3LYP and LMP2 results ar e: closer to experiment but are still underestimates. Structures optim ized at the B3LYP level are in good agreement with experimental geomet ries. The results are encouraging with regard to the ability of suitab le quantum chemical methods to accurately treat the dative bonding imp ortant for a reliable description of molecule-surface interactions. (C ) 1997 Elsevier Science B.V.