Estrutura eletrônica em materiais bidimensionais: dicalcogenetos de metal de transição (TMDS) e bicamada de sílica (SiO2)

Abstract

In this work by using a first principles methodology, in the framework of the Density Functional Theory (DFT), three problems are addressed: in the first place, a study of electronic structure and phonon modes of transition metal dichalcogenides (TMDs) monolayers (MoS2,MoSe2 e MoT e2), is presented. Band structures, energy gaps and normal modes of vibration are calculated in good agreement with experimental results.Normal modes and phonon dispersion curves are obtained in the scheme of Density Functional Perturbation Theory (DFPT) proposed by S. Baroni.et.al. As a second part, the energy barrier for the formation of Stone-Wales (SW) defects in silica (SiO2) is estimated, using a Nudged Elastic Band Method (NEB) as implemented in the VASP software. Finally, preliminary steps of a study of tilt grain boundaries (GB) in TMDs, are presented. The geometries considered in this work are based on the so-called 5-7 defect, that constitutes the periodic unit of the grain boundaries. Such geometries may explain the tilt angle experimentaly observed in policrystaline samples.