Determining the electronic and magnetic structure of strongly correlated systems is a difficult task, but of crucial importance. In this project, we will investigate several strongly correlated systems, mainly by means of a combination of density functional theory and dynamical mean-field theory (DFT+DMFT). We intend first to apply a method that we recently developed to calculate the strength of the Coulomb interactions in various solids containing lanthanides. After an initial investigation on the elemental lanthanides, we plan to explore lanthanides compounds as well. We can join the information obtained through our method to enrich the predictive properties of big-data analyses, such as those performed in our recent work on Physical Review Materials 1, 033802 (2017). Families of Pr or Sm compounds are very interesting (respectively, for magnetism and valence stability) and are likely to lead to interesting discoveries. We will also apply our new method to obtain reliable parameters to investigate magnetism at atomic scale, as e.g. in lanthanide adatoms deposited on graphene (and other 2-dimensional materials). Experimental data measured via scanning tunneling spectroscopy (STS, provided by our experimental colleagues) show features that are difficult to explain without a reliable theoretical support. To this aim we intend to perform various DFT+DMFT calculations, including different settings, substrates and geometrical configurations.
Furthermore, we will investigate the electronic properties of two classes of strongly correlated materials: 1) semiconductors doped with magnetic impurities, like (Mn,Ga)As or (Cr,Ga)As; 2) topological insulators doped with magnetic impurities, like (Cr,Bi)2Se3. The magnetic order arising in these two classes of materials is still not fully understood and this understanding is necessary if we want to engineer materials whose magnetism persists at room temperature. Our project intends to address all these issues through DFT+DMFT calculations. Disorder will be included at the level of special quasi-random structures (SQS), which require large supercells and therefore a large computational effort. We will perform analyses of the inter-atomic exchange interactions and X-ray absorption spectra, using our recently proposed method [Physical Review B 96, 245131 (2017)].
Finally, a third line of research is focused on the formation of charge density waves in layered transition metal dichalcogenides.The recent discovery of layer-mismatch-induced superconductivity lead to a renewed interest in 2-dimensional transition metal Charge density waves are closely related to superconductivity and are therefore worth investigating. Our proposed plan of research comprises a series of first-principles calculations of selected 2-dimensional transition metal dichalcogenides, as e.g. NbSe2 and TaSe2, deposited on graphene or analogous substrates (honeycomb materials). Electronic structure and phonon spectra obtained via standard DFT are going to clarify what conditions affect the formation and stability of charge density waves. Despite these calculations do not involve sophisticated many-body techniques, their computational cost is expected to be very high, since the systems to investigate are very large and the accuracy required to resolve small energy differences is very high.