  By using the density functional theory method, we systematically study the
influences of the doping of an Al atom on the electronic structures of the
Mg(0001) surface and dissociation behaviors of H2 molecules. We find that for
the Al-doped surfaces, the surface relaxation around the doping layer changes
from expansion of a clean Mg(0001) surface to contraction, due to the
redistribution of electrons. After doping, the work function is enlarged, and
the electronic states around the Fermi energy have a major distribution around
the doping layer. For the dissociation of H2 molecules, we find that the energy
barrier is enlarged for the doped surfaces. Especially, when the Al atom is
doped at the first layer, the energy barrier is enlarged by 0.30 eV. For
different doping lengths, however, the dissociation energy barrier decreases
slowly to the value on a clean Mg(0001) surface when the doping layer is far
away from the top surface. Our results well describe the electronic changes
after Al-doping for the Mg(0001) surface, and reveal some possible mechanisms
for improving the resistance to corrosion of the Mg(0001) surface by doping of
Al atoms.
