  We present an orbital-resolved density functional theory study on the
electronic properties of hydrogen and lithium intercalated graphene grown on
the Si face of SiC. Starting from the $(6\sqrt3\times6\sqrt3)R30^{\circ}$
surface reconstruction of the graphene/SiC heterosystem, we find that both H
and Li can restore the ideal structural characteristics of the two
nonequivalent junction parts (i.e. graphene and the SiC substrate) when
inserted at the interface. However, the chemical/electrostatic interactions
remain different for the two cases. Hence, H-intercalated epitaxial graphene is
subject to a sublattice symmetry-breaking electronic interference that perturbs
the Dirac point, whereas Li intercalation gives rise to a highly $n$-doped
system due to a nonuniform delocalization of Li charges. Results bring to
discussion the role of substrate engineering in epitaxial graphene on SiC.
