  Graphene has received a great deal of attention and this has more recently
extended to boron nitride sheets (BNS) with a similar structure. Both have
hexagonal lattices and it is only the alternation of atoms in boron nitride,
which changes the symmetry structure. This difference can for example be seen
in the mean field equations, which for the corners of the Brillouin Zone are
Dirac equations. For the case of graphene (equal atoms) we have the equation
for massless particles, while for Boron Nitride has a finite gap and is more
near a Dirac equation with mass near this gap.. Carbon structures in general
and in particular also graphene can adsorb electron donors, such as alkaline
atoms or molecules with a dipole moment. Typically these atoms and the dipoles
can only attach in the sense to donate electron density. Some results for small
sheet like structures are available.
