First-Principles Study of the Atomic and Electronic Structure of Twisted Bilayer Graphene

Twisted bilayer graphene (tBLG) has garnered significant attention due to the emergence of strong electron-electron correlations at small twist angles within the “magic angle” range, leading to superconductivity and other exotic behavior. While some studies have previously characterized the flat bands of tBLG at the magic angle using ab initio methods, the majority of efforts to describe the atomic and electronic structure of tBLG have relied on effective continuum models. In this work, we present a comprehensive and detailed study of the atomic and electronic structure of tBLG over a large range of twist angles, including the magic angle, based fully on density functional theory (DFT). While the main features of the atomic and electronic structure obtained from the DFT calculations agree with those predicted from effective models, there are several aspects that deserve closer examination for which we provide a detailed discussion. Our results also allow us to make contact with experimental measurements like scanning tunneling microscopy (STM) studies. Finally, based on the realistic wavefunctions we obtain, we provide values for various parameters that are relevant to many-body models for correlated electron behavior in tBLG, as a function of the twist angle.