First principle study of WTe2 from monolayer to bilayer and bulk

We use density functional theory (DFT) to calculate the total energy of a series of monolayer transition metal dichalcogenides, for three phases 1H (hexagonal), 1T (orthorhomibic) and 1T' (orthorhomibic). We find the ground state of MoTe2, CrTe2 and WTe2 is 1T', the energy of which is very close to 1T; for ScTe2, VTe2, ReTe2 the ground state is 1T; for TiTe2 and HfTe2 the ground state is 1H. We verify for WTe2, 1T and 1T' is connected by the band inversion. We calculate the dielectric function of monolayer, bilayer and the bulk Td phase of WTe2, and find the average dielectirc constant (zero frequency limit) increses from 8.08 to 21.82 (bilayer) and 48.6 (bulk), although they have strong anisotropy along a, b and c axis. The software we use is DS-PAW (Device studio-projector augmented wave) developed by Hongzhiwei Technology (Shanghai) Co. Ltd. The Perdew-Burke-Ernzerhof (PBE) exchange-correlation energy functional within the generalized gradient approx imation (GGA) were employed.