On the role of relativistic effects on the structural, physical and chemical properties of molecules and materials

I have chosen to detail only my research works that relate to one well-identified common theme: 'Role of relativistic effects on the properties of molecules and materials'. Therefore, only the publications for which the computed property vanishes in the absence at least one relativistic interaction, or the ones in which the role of at least one relativistic term on a given property is determined, will be discussed. The only exception to this rule concern one publication related to photophysics [article no. 22]. The chapters have been defined according to research topics and not to the quantum mechanical methodologies that were followed. Chapter 2 focusses on molecular and solid state magnetism. Note that in all the studies that will be reported, spin-dependent relativistic effects were introduced a posteriori. Chapter 3 focusses mainly on 'applied' theoretical radiochemistry, in the sense it essentially deals with the outcomes of quantum mechanical calculations that were performed to address experimental concerns, for interpretation and/or prediction purposes. Although two-step WFT approaches have also been used in this context, most of the reported results were based on DFT. A more fundamental aspect of theoretical radiochemistry concerns the development and application of chemical bonding analysis tools that are valid for heavy-(radio)element species, i.e. analysis tools applicable on top of DFT or WFT calculations that does include SOC, a priori or a posteriori. This will be the subject of Chapter 4 (results) and Chapter 5 (prospects). Interestingly, the two-step approach is the bridge between all the chapters, and I hope that this manuscript will convince the readers of the interest of using this approach in various contexts