Interlayer Coupling and Doping Effects in Te-based Transition Metal Dichalcogenides: Insights from Quantum Monte Carlo and DFT Calculations

Transition metal dichalcogenides containing tellurium (Te) have attracted a great deal of attention, primarily due to their unique electronic and optical properties, which arise from strong Te-Te interlayer interactions. In this study, we explored these materials using quantum Monte Carlo (QMC) simulations, specifically focusing on VTe₂ and its Janus counterpart, VSTe. Initially, we optimized the geometric structures of monolayer VTe₂ and VSTe, which revealed that DFT-PBE geometry relaxation calculations tend to overestimate their lattice parameters, compared to those optimized through QMC. Subsequent PBE+U calculations, based on the QMC-optimized geometries, indicated a potential transition from a direct to an indirect band gap in 2H-VTe₂ via the substitution of V with either tantalum (Ta) or niobium (Nb). In addition, significant band gap opening was observed in 2H-VSTe upon Ta or Nb doping. We will also discuss how Te-Te interlayer coupling and dopant incorporation influence the electronic and optical properties of bilayer VTe₂, employing insights from both QMC and PBE+U calculations.