Exploring interlayer coupling in the twisted bilayer PtTe₂ via quantum Monte Carlo methods

We investigated interlayer interactions in bilayer PtTe₂, focusing on their influence on the electronic energy bands near the Fermi level. Our diffusion Monte Carlo (DMC) calculations for high-symmetry bilayer stackings (AA, AB, AC) reveal distinct interlayer binding characteristics, with significant variations in interlayer separation across different stacking modes. These differences are crucial for understanding the interlayer coupling in twisted bilayers with diverse local stacking arrangements.

A comparison of interlayer separations from DMC and density functional theory (DFT) shows that van der Waals–DFT with meta-generalized gradient approximation (GGA) aligns well with DMC results across multiple stackings, including twisted bilayers. However, only the ground-state AA stacking matches closely with GGA-based DFT predictions, highlighting the need for accurate exchange-correlation potentials to capture stacking-dependent interlayer binding properties.

We further demonstrate that discrepancies in DFT-predicted interlayer separations contribute to significant differences in the band structures of the 21.79° twisted bilayer PtTe₂, affecting its classification as metallic or insulating. These findings emphasize the importance of accurately modeling stacking-dependent interlayer coupling for understanding delicate bilayer systems at finite twists.