In pursuit of accurate interlayer potentials for twisted bilayer graphynes

Recent explorations of twist in bilayer graphene and the discovery of superconducting phases at certain magic angles have laid the groundwork for a new branch in materials science called twistronics. However, theoretical studies on twisted layered materials are impeded due to the computational expense associated with first-principles calculations. Empirical force field approaches that include anisotropic terms to describe interlayer interactions have come to the fore as excellent alternatives to deal with such a stumbling block. Taking a cue from these formulations, herein, we describe our pursuit of capturing the interlayer interactions in bilayer graphynes with atomistic empirical potentials. The choice of the potentials, namely the improved Lennard-Jones potential and Hod's interlayer potential, is motivated by the objective of bringing out the role of anisotropy explicitly. Empirical parameters for both the potentials are calibrated against dispersion-corrected DFT calculations that are performed to incorporate the stacking, sliding and twisting features of the bilayer configurations. Although the isotropic improved Lennard-Jones potential is able to describe the interlayer stacking of graphynes, it is inadequate to account for the interlayer twist properties. The anisotropic Hod's interlayer potential portrays the interlayer twisting energy profiles of the benchmark DFT calculations with a reasonable accuracy. Our potential formulations can bestow impetus to the research on the homo- and hetero-bilayer structures of graphynes and other two-dimensional materials.