▎ 摘　　要

Using ab initio calculations, we systematically investigate graphene nucleation on 10 representative metal substrates that have been used in graphene growth by chemical vapor deposition. We find that the metal substrates can be divided into three categories with respect to the competition between carbon carbon (C-C) and carbon metal (C-M) interactions, which leads to the distinct critical size (N-c) dependence of the smallest graphene precursor on the substrates. The C-M interactions are weak on Ag, Au, Cu, and Co substrates, and the chemical potential of carbon decreases monotonically to approach that of graphene as the size of the carbon clusters increases. We observed an N-c around C-13-C-14 corresponding to the structural transition from a linear chain to sp(2) configuration on these substrates. In contrast, the C-M interactions are strong on Ru, Pt, Rh, and Ir substrates, and the extremely stable carbon monomerr-therm-odynarnically determines the larger N-c about C-19. The third category is Ni and Pd substrates, for which carbon atoms tend to penetrate into the first layer of the metal substrates, implying a more complicated graphene nucleation mechanism. We:also discuss the growth kinetics of the small carbon dusters as well as the effect of the practical environment,: like surface defects, on graphene nucleation.