Effetto dell'Accoppiamento Spin-Orbita sulle Proprietà Strutturali ed Elettroniche del Semiconduttore Layered Rashba BiTeI

This thesis was carried out in the Theoretical chemistry group of the University of Torino, where CRYSTAL, a package for ab initio solid state simulations, is developed. The work presented shows an application of recent Spin-Orbit Coupling (SOC) implementations in CRYSTAL on the layered semiconductor BiTeI, where all three atoms are treated relativistically. SOC has a significant effect on the electronic structure of BiTeI, leading to the splitting of valence and conduction bands. The objective of this thesis is to account in a fully consistent way for the large SOC effect of BiTeI, with a two-component relativistic approach. This results in the inclusion of SOC in the orbital relaxation, at every cycle of the self-consistent field procedure (SCF). Furthermore, this work seeks to quantify other subtle effects, such as spin currents. The approach used fits into the framework of Spin-Current Density Functional Theory (SCDFT), which becomes necessary when describing these relativistic effects and implies the development of DFT exchange-correlation functionals that adhere to physical constraints. Finally, this work aims to describe BiTeI's connection between its crystal and electronic structures, considering its layered structure. The influence of long-range vdW interactions is decisive for the interlayer distance and the magnitude of SOC.