By using density-functional theory (DFT) calculations, the dissociation of CH on various metal surfaces, including Ni, Cu, Ru, Pd, Pt, Ir, Co, Au, and Rh, is systematically explored. For all the explored face-centered cubic (fcc) metal substrates, the (100) surface is found to be more active than the (111) surface, which explains the higher activity of the (100) surface in graphene chemical vapor deposition (CVD) growth. The catalytic activity order of these metals is found to be Ni ≈ Rh ≈ Co ≈ Ru > Pd ≈ Pt ≈ Ir > Cu > Au, which explained the catalyst type dependent growth behavior of graphene. It was found that the main dissociation product of CH on Ni, Pd, Pt, Ir, Rh, Co, and Ru substrates is a carbon monomer and a very high rate of dissociation is expected, but a low rate of dissociation and the dissociation products of CH (i = 1, 2, 3) are expected on Cu and Au surfaces, which explained the diffusion-limited growth of graphene on Cu and Au surfaces and attachment limited growth on other active metal surfaces. Furthermore, our study shows that the dissociation of CH on all these metal substrates follows the well-known Brønsted-Evans-Polanyi (BEP) principles, or the reaction barrier is roughly linear to the reaction energy.

The cycloaddition chemistry of several representative unsaturated hydrocarbons (1,3-butadiene, benzene, ethylene, and acetylene) and a heterocyclic aromatic (thiophene) on a Si(111)-7x7 surface has been explored by means of density functional cluster model calculations. It is shown that (i) 1,3-butadiene, benzene, and thiophene can undergo both [4+2]-like and [2+2]-like cycloadditions onto a rest atom-adatom pair, with the former process being favored over the latter both thermodynamically and kinetically; (ii) ethylene and acetylene undergo [2+2] cycloaddition-like chemisorptions onto a rest atom-adatom pair; and (iii) all of these reactions adopt diradical mechanisms. This is in contrast to the [4+2] cycloaddition-like chemisorptions of conjugated dienes on a Si(100) surface and to the prototype [4+2] cycloadditions in organic chemistry, which were believed to adopt concerted reaction pathways. Of particular interest is the [4+2]-like cycloaddition of s-trans-1,3-butadiene, whose stereochemistry is retained during its chemisorption on the Si(111) surface.

Systematic density functional cluster model calculations reveal that the [2 + 2] cycloadditions of ethylene on the (100) surfaces of group IV semiconductors (silicon, germanium, and diamond) follow diradical mechanisms. Details of the reaction pathways vary subtly with the bonding nature of the surface dimers, including their zwitterionicity, weakness of their π-bond, and readiness to react as a diradical.