Towards accurate ionic relaxation algorithms for two-dimensional chalcogenide van der Waals materials - A first-principles study

Abstract

Recently, two-dimensional (2D) layered materials, known as van der Waals (vdW) materials, have attracted remarkable attention due to their unique electrochemical and physical properties. Transition metal dichalcogenides (TMDs) are 2D materials, which commonly exist in three polymorphs (1T, 2H, and 3 R) in a honeycomb structure (hexagonal lattice). From a structure relaxation point of view, the 1T phase has less structural symmetry along the z-direction, rendering it more challenging than the 2H counterpart. Herein, the importance of enabling vdW forces as well as the associated challenges during the simulation of 1T polymorph are tackled. The two most widely used ionic relaxation methods (conjugate gradient and RMM-DIIS) were used for six TMDs (TaS2, TaSe2, MoS2, MoSe2, WS2, WSe2), and the results were compared to those reported in the literature. Moreover, a newly designed advanced conversion algorithm (TPSCA) is developed by incorporating shell scripts, DFT electronic relaxation, and Python coding. The developed algorithm is tested for 1T-TaS2 to confirm the obtained results and get better insights into the dependence of the energy on the different combinations of those parameters.