Assessing the accurate exchange-correlation functional in van der Waals TMD Materials AB2 (A = Nb, Ta and B = S, Se, Te)

Two-dimensional (2D) transition metal dichalcogenides (TMDs) exhibit diverse functionalities owing to their highly tunable chemical, physical, and electronic attributes. In this study, we systematically investigate the structural, electronic, and phonon responses of six TMD systems using density functional theory (DFT) simulations. Our analysis unveils a reversible phase transition between the semiconducting (2H) and metallic (1T) phases within the stable phases of these TMD systems. Specifically, group-V TMDs (AB 2, where A = Nb, Ta and B = S, Se, Te) systems are focused in the present calculations. Their electronic behavior has been evaluated to validate the accuracy of several available exchange-correlation (XC) functionals, along with van der Waals density functionals (vdW-DFs). Both spin-orbit coupling (SOC) effects and non-SOC (NSOC) cases are considered in our calculations. Notable changes in the electronic band structure and density of states between the 2H and 1T phases underscore their potential utility in conventional device applications.