  We studied the real space structure of states in twisted bilayer graphene at
the `magic angle' $\theta = 1.08^\circ$. The flat bands close to charge
neutrality are composed of a mix of `ring' and `center' orbitals around the AA
stacking region. An effective model with localized orbitals is constructed,
which necessarily includes more than just the four flat bands. Long-range
Coulomb interaction causes a charge-transfer at half-filling of the flat bands
from the `center' to the `ring' orbitals. Consequently, the Mott phase is a
featureless spin-singlet paramagnet. We estimate the effective Heisenberg
coupling that favors the singlet coupling to be $J = 3.3$ K, consistent with
experimental values. The superconducting state depends on the nature of the
dopants: hole-doping yields $p+ip$-wave whereas electron-doping yields
$d+id$-wave pairing symmetry.
