Theoretical studies of chemical reactions on surfaces and on fullerene models

This project encompasses three applications of density functional theory electronic structure calculations to the study of chemical reactions. In the first project, we examine the local 3 x 1 → 2 x 1 rearrangement of the Si(100)-3 x 1:H surface following the loss of two H atoms induced by an STM tip. This interesting rearrangement of the Si(100)-3x1:H surface consists of a series of bond breaking, bond-forming and hydrogen hopping steps. We investigated the rearrangement using density functional theory calculations with the PW91 functional and the nudged elastic band algorithm for finding transition states. We estimate that the 3 x 1 → 2 x 1 rearrangement has overall barriers ranging from 0.1 to 1.6 eV, depending on the sites from which the H atoms are lost.; In the second project, we make concerted use of slab and cluster models to study H₂ desorption from a single dimer of the Si(100)-2 x 1 surface. The largest cluster model considered, Si₈₉H₆₂, contains eight surface dimers and gives reaction and activation energies for desorption nearly identical to the slab-model values when the same electronic structure method is used. The barrier for H₂ desorption, calculated using the Si₈₉H₆₂ cluster model and the Becke3LYP functional, is 64.3 kcal/mol. When this result is corrected for the effects of basis set expansion and vibrational zero-point energy correction, the barrier decreases to about 61.0 kcal/mol, which is only 4.0 kcal/mol greater than the observed desorption barrier.; In the third project, electronic structure calculations are used to study the addition of oxygen atom to circumtrindene. Circumtrindene, a C₃₆ H₁₂ open geodesic dome with alternating five- and six-membered rings, is considered as a model for the cap of a single-walled carbon nanotube. O-atom addition to a C-C bond shared between the central and adjacent hexagons gives an epoxide structure while O-atom addition to a C-C bond shared by the central hexagon and an adjacent pentagon results in cleavage of the C-C bond and an R-O-R insertion product. The two oxidation products are predicted to be of comparable stability with a large (55.7 kcal/mol) barrier for interconversion.