A Single Twist Angle Selection Method for Bilayer Materials

Twist-averaging (TA) is used to improve accuracy of results for methods like coupled cluster singles and doubles (CCSD) by averaging many calculations at different twist angles. However, running multiple CCSD calculations is costly. The structure factor twist averaging (sfTA) approach uses the transition structure factor (TSF), which is related to the electronic correlation energy, to find a single twist angle that approaches TA accuracy. This has been shown effective for 3D bulk solids, reducing cost to about a single CCSD calculation. In this work we expand the sfTA method to 2D bilayer solids. This allows us to calculate TA-level interlayer binding energies for a variety of materials at a reduced computational cost. This is accomplished by defining a binding TSF analogous to the original TSF, which relates the change in the electronic structure between a monolayer and a corresponding bilayer. We compare the binding energies for the sfTA, binding sfTA, and TA methods in addition to a single CCSD calculation run at the Γ-point. Our new binding sfTA method shows good agreement with TA for the calculated binding energy, consistent with the observations found for original sfTA. Additionally, we investigate the sensitivity of the method to the choice of special twist angle for the binding energies using contour maps across the twist angle coordinates.