THEORETICAL-STUDY OF THE BINDING-ENERGY AND BONDING OF BENZENE TO THENI (111), (100), AND (110) SURFACES

The atomic superposition electron delocalization molecular orbital (AS ED-MO) method has been applied to a study of the favored bonding sites for benzene adsorbed on the (111), (100), and (110) crystal faces of nickel metal. The different faces were represented in the calculations by clusters, which contained 30 nickel atoms. By using the same size clusters and parameters, it was possible to compare the results among the three different crystal faces. The most favored (highest binding e nergy) sites for the benzene ring parallel to the surface were found t o be the highest coordination site for the (111) and (100) planes and the atop site for the (110) plane. These results are compared with bot h experimental and other theoretical calculations on these crystal pla nes. In addition, the bonding of the benzene to the Ni surfaces has be en investigated by using ''bonding plots'', which are graphical repres entations of the Mulliken population matrix. By use of these bonding p lots, a picture of the bonding of the benzene to the nickel surface is developed and an explanation for the increase of the binding energy w ith increased cluster size is discussed.