Accurate force-field methodology capturing atomic reconstructions in transition metal dichalcogenide moir\'e systems

TL;DR

This paper introduces a generalized force-field approach for accurately modeling atomic reconstructions in large twisted transition metal dichalcogenide heterostructures, enabling efficient relaxation and analysis of their moiré patterns.

Contribution

The authors develop a transferable force-field parameterization that reproduces DFT results for large moiré systems, facilitating detailed structural and electronic analysis.

Findings

Force-field parameters achieve <20 meV accuracy in band structure comparison with DFT.

Relaxation significantly alters the moiré potential, making it deeper and wider.

Atomic reconstruction is prominent at twist angles below 4-5 degrees.

Abstract

In this work, a generalized force-field methodology for the relaxation of large moir\'e heterostructures is proposed. The force-field parameters are optimized to accurately reproduce the structural degrees of freedom of some computationally manageable cells relaxed using density functional theory. The parameters can then be used to handle large moir\'e systems. We specialize to the case of 2H-phased twisted transition-metal dichalcogenide homo- and heterobilayers using a combination of the Stillinger-Weber intralayer- and the Kolmogorov-Crespi interlayer-potential. Force-field parameters are developed for all combinations of MX$_2$ for $\text{M}\in\{\text{Mo},\text{W}\}$ and $\text{X}\in\{\text{S},\text{Se},\text{Te}\}$. The results show agreement within 20 meV in terms of band structure between density functional theory and force-field relaxation. Using the relaxed structures, a simplified and systematic scheme for the extraction of the interlayer moir\'e potential is presented for both R- and H-stacked systems. We show that in-plane and out-of-plane relaxation effects on the moir\'e potential, which is made both deeper and wider after relaxation, are essential. An interpolation based methodology for the calculation of the interlayer binding energy is also proposed. Finally, we show that atomic reconstruction, which is captured by the force-field method, becomes especially prominent for angles below 4-5$^\circ$, when there is no mismatch in lattice constant between layers.