Caracterização de estados de carga de defeitos em sistemas bidimensionais por primeiros princípios: abordagens para os problemas metodológicos

Abstract

In this dissertation, we study the problem of determining formation and transition energies between charge states of defects in two-dimensional materials through calculations based on Density Functional Theory. The problem presents methodological difficulties associated with the use of supercells that periodically repeat in space in calculations of electrically charged systems. In two-dimensional materials, in particular, vacuum in one direction accentuates problems related to the lack of electrostatic shielding, leading to divergences in the determination of total energy and spurious behaviors of the convergence of the values of physical quantities with the size of the cell. We present three approaches discussed in the literature to address this issue. We then choose one of them for a particular application that consisted of studying the double vacancy of $Si$ and $C$ in a two-dimensional silicon carbide system ($SiC$). This representative example illustrates both the need for correction for the determination of the transition energies between charge states of the defect and the methodological steps involved in implementing the correction.