  Close to a magical angle, twisted bilayer graphene (TBLG) systems exhibit
isolated flat electronic bands and, accordingly, strong electron localization.
TBLGs have hence been ideal platforms to explore superconductivity, correlated
insulating states, magnetism, and quantized anomalous Hall states in reduced
dimension. Below a threshold twist angle ($\sim$ $1.1^\circ$), the TBLG
superlattice undergoes lattice reconstruction, leading to a periodic moir\'e
structure which presents a marked atomic corrugation. Using a tight-binding
framework, this research demonstrates that superlattice reconstruction affects
significantly the electronic structure of small-angle TBLGs. The first magic
angle at $\sim$ $1.1^\circ$ is found to be a critical case presenting globally
maximized electron localization, thus separating reconstructed TBLGs into two
classes with clearly distinct electronic properties. While low-energy Dirac
fermions are still preserved at large twist angles $> 1.1 ^\circ$, small-angle
($\lesssim 1.1^\circ$) TBLG systems present common features such as large
spatial variation and strong electron localization observed in unfavorable AA
stacking regions. However, for small twist angles below $1.1 ^\circ$, the
relative contribution of the local AA regions is progressively reduced, thus
precluding the emergence of further magic angles, in very good agreement with
existing experimental evidence.
