  The geometric and electronic properties of Bi-adsorbed monolayer graphene,
enriched by the strong effect of substrate, are investigated by
first-principles calculations. The six-layered substrate, corrugated buffer
layer, and slightly deformed monolayer graphene are all simulated. Adatom
arrangements are thoroughly studied by analyzing the ground-state energies,
bismuth adsorption energies, and Bi-Bi interaction energies of different adatom
heights, inter-adatom distance, adsorption sites, and hexagonal positions. A
hexagonal array of Bi atoms is dominated by the interactions between the buffer
layer and the monolayer graphene. An increase in temperature can overcome a
$\sim 50$ meV energy barrier and induce triangular and rectangular
nanoclusters. The most stable and metastable structures agree with the scanning
tunneling microscopy measurements. The density of states exhibits a finite
value at the Fermi level, a dip at $\sim -0.2$ eV, and a peak at $\sim -0.6$
eV, as observed in the experimental measurements of the tunneling conductance.
