Interlayer couplings in homobilayer structures of M Si 2 X 4 (M = Mo, W; X = N, P, As)

We investigated the interlayer coupling effect in homobilayer structures of MSi2X4 with M = Mo, W and X = N, P, As. Through the combination of first-principles calculations and analytical formulations, the equilibrium interlayer distance, layer energy difference, and interlayer hopping strength are obtained for all six MSi2X4 materials, which are found to be insensitive to the type of M atom but differ significantly between X = N and X = P, As. In homobilayers with twist angles close to 0, the interlayer charge redistribution introduces a stacking-dependent interlayer electrostatic potential with a magnitude reaching 0.1 eV in MSi2N4, suggesting that it can be an excellent candidate for studying the sliding ferroelectricity. The interlayer hopping strengths are found to be as large as several tens meV at valence band maxima positions K and T, and similar to 1 meV at the conduction band edge K. The resultant layer hybridizations vary in a large range under different stacking registries, which can be used to simulate honeycomb lattice models with both trivial and nontrivial band topologies.