@article {carr2019exact, title = {Exact continuum model for low-energy electronic states of twisted bilayer graphene}, journal = {Physical Review Research}, volume = {1}, number = {1}, year = {2019}, pages = {013001}, publisher = {APS}, doi = {10.1103/PhysRevResearch.1.013001}, author = {Carr, Stephen and Fang, Shiang and Zhu, Ziyan and Efthimios Kaxiras} }