**Relaxation effects in twisted bilayer graphene: A multiscale approach**

N Leconte and S Javvaji and JQ An and A Samudrala and JL Jung, PHYSICAL REVIEW B, 106, 115410 (2022).

DOI: 10.1103/PhysRevB.106.115410

We present a multiscale density functional theory (DFT) informed molecular dynamics and tight-binding approach to capture the interdependent atomic and electronic structures of twisted bilayer graphene. We calibrate the flat band magic angle to be at theta(M) = 1.08 degrees by rescaling the interlayer tunneling for different atomic structure relaxation models as a way to resolve the indeterminacy of existing atomic and electronic structure models whose predicted magic angles vary widely between 0.9 degrees and 1.3 degrees. The interatomic force fields are built using input from various stacking and interlayer distance-dependent DFT total energies including the exact exchange and random phase approximation (EXX-PRPA). We use a Fermi velocity of u(F) similar or equal to 10(6) m/s for graphene that is enhanced by similar to 15% over the local density approximation (LDA) values. Based on this atomic and electronic structure model we obtain high-resolution spectral functions comparable with experimental angle-resolved photoemission spectroscopy. Our analysis of the interdependence between the atomic and electronic structures indicates that the intralayer elastic parameters compatible with the DFT-LDA, which are stiffer by similar to 30% than widely used reactive empirical bond order force fields, can combine with EXX-PRPA interlayer potentials to yield the magic angle at similar to 1.08 degrees without further rescaling of the interlayer tunneling.

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