  A theoretical framework, which is under the first-principles calculations, is
developed to fully explore the dramatic changes of essential properties due to
the silicon-atom chemical modifications on monolayer graphenes. For the
Si-chemisorption and Si-substituted graphenes, the guest-atom-diversified
geometric structures, the Si- and C-dominated energy bands, the magnetic
moments, the charge transfers, the spatial charge densities, the spin
distribution configurations, and the van Hove singularities in the atom- and
orbital-projected density of states are investigated thoroughly by the delicate
evaluations and analyses. Such fundamental properties are sufficient in
determining the critical physical and chemical pictures, in which the accurate
multi-orbital hybridizations are very useful in comprehending the diverse
phenomena, e.g., the C- and Si-co-dominated energy bands, the semiconducting or
metallic behaviors, and the existence/absence of Dirac-cone band structures.
This developing model could be generalized to other emergent layered materials.
