Density Functional Theory

Since its theoretical foundation in the mid-1960’s, Density Functional Theory (DFT) is being used in computational solid state physics to calculate structural, magnetic and ground state properties of real materials from first principle1 .
In this thesis we will use Density Functional Theory to study different perovskites materials. A short introduction for each subject is given here, a more elaborated one at the beginning of the respective chapters.
The first study is devoted to oxygen vacancies in SrTiO3 with different concentrations by means of first-principles simulations. These types of point defect represent very common imperfections in ABO3 -type perovskite oxides diversifying their chemistry and leading to a broad range of possible technological

One of these cases the so-called inverse perovskite (anti-perovskite). Intermetallic antiperovskites closely related to MgCNi3 are therefore subject to investigations, both in the search for new superconductors and in the pursuit of a better understanding of the interplay between superconductivity and magnetism. It was suggested that carbon-containing antiperovskites may be good candidates. Systematic investigation of the synthesis and fundamental properties of nonoxide perovskite-type compounds is necessary. The ternary carbides of rare-earth metal R-Rh-C system have also received considerable attention in the superconductivity and magnetism field. So, most interest is limited to the synthesization and structural analysis and the absence in the literature of any information about the ab-initio electronic and magnetic structure of these compounds has led us to study these new materials. And for comparison with Ref. [12], the magnetic stability of RRh3 C compounds for R = La, Ce, Pr, Nd, Pm,

The aim here is to introduce the models used for the study of the bulk of the materials investigated during this thesis.
Chapter 3 is divided in two principle sections. In the first section we outline the basic foundations of the ground-state density functional theory. We introduce the Hohenberg-Kohn theorem and the Kohn-Sham equations and finally we describe superficially the main approximations for the exchange-correlation functional. In the second section we highlight in detail the main computational method FP-LAWP+lo used in our simulations and the numerical parameters used during the whole thesis.
In chapter 4 a current knowledge of material perovskites properties is briefly presented. Chapter 5 show a detail investigation of the electronic structure and nature of bonding around the oxygen vacancies in SrTiO3