Comparison of band-fitting and Wannier-based model construction for WSe2

Abstract

Transition metal dichalcogenide materials MX2(M = Mo, W;X = S,Se) are being thoroughly studied due to their novel two-dimensional structure, that is associated with exceptional optical and transport properties. From a computational point of view, Density Functional Theory simulations perform very well in these systems and are an indispensable tool to predict and complement experimental results. However, this technique has a significant restriction since it can only be applied at zero temperature and, given that it can only deal with a relatively small number of atoms, its ability to treat, for example, electron-lattice coupling when studying excitation states is limited. Multi-scale techniques, like the recently proposed Second Principles Density Functional Theory, can go beyond these limitations but require the construction of tight-binding models for the systems under investigation. In this work, we compare two such methods to construct the bands of WSe2. In particular, we compare the result of (i) Wannier-based model construction with (ii) the band fitting method of Liu et al.,1 where the top of the valence band and the bottom of the conduction band are modeled by three bands symmetrized to have mainly Tungsten dz2, dxy and dx2−y2 character. Our results emphasize the differences between these two approaches and how band-fitting model construction leads to an overestimation of the localization of the real-space basis in a tight-binding representation.