Title:	Strong electronic correlations and magnetism in systems containing transition metals and lanthanides
DNr:	SNIC 2019/3-580
Project Type:	SNIC Medium Compute
Principal Investigator:	Igor Dimarco <igor.dimarco@physics.uu.se>
Affiliation:	Uppsala universitet
Duration:	2019-11-08 – 2020-12-01
Classification:	10304 10407
Homepage:	http://fplmto-rspt.org/
Keywords:

Abstract

In this project, we plan to use density functional theory (DFT) and its combination with dynamical mean field theory (DMFT) to investigate various problems, grouped in three major lines of research. Our first line of research is focused on understanding how the formation of charge density waves in layered transition metal dichalcogenides can be controlled via external means. Systems of interest include NbSe2 and TaSe2, both in bulk and monolayer form, deposited on graphene or generic honeycomb materials. Electronic structure and phonon spectra obtained via DFT are going to clarify what conditions affect the formation and stability of charge density waves. In presence of impurities, the formation of long range magnetic order will be investigated through the analysis of inter-atomic exchange interactions and magnetic models. The competition between magnetism and charge density waves under isotropic and uni-axial strain will also be investigated. Our second line of research is focused on understanding the magnetic and electronic properties of Lanthanide adatoms deposited on graphene. Experimental data measured via scanning tunneling spectroscopy (STS, provided by experimental colleagues at EPFL) show features that are difficult to explain without theoretical support. To understand these systems we intend to perform various DFT+DMFT calculations, for different substrates and geometrical configurations. Recent technical developments of our in-house code RSPt will be used to calculate the intra-atomic exchange interactions, which we believe drive the phenomena observed in STS. These systems are also a good playground to solve a crucial methodological problem in the physics of the Lanthanides, i.e. the first-principles calculations of crystal field levels (via DFT+DMFT). Finally, our third line of research is focused on complex oxides. An important problem here is the role played by O-vacancies on the electronic properties of FeO, CoO and CeO2. In a previous work [Physical Review Letters 109, 186401; 2013] we showed that DFT+DMFT calculations can reproduce the photoemission spectra of the transition metal mono-oxides with a great accuracy. Nevertheless, some discrepancies are found for FeO and CoO, most likely due to the formation of clusters with a different stoichiometry. In this project, we intend to understand the role of clustering in these systems. Calculations for different concentrations of O vacancies will be performed using special quasi-random structures (SQS), which require large supercells and therefore a large computational effort. O vacancies are also important for practical applications of CeO2. In fact, most of the useful properties of "ceria" are related to the O transport via hopping of an O vacancy. An interesting feature here is that the localized-itinerant character of the Ce-4f electrons is significantly affected by its local environment, and therefore the electronic structure is expected to lead to drastic changes. For complex oxides, we will also perform analyses of the inter-atomic exchange interactions and X-ray absorption spectra, using our recently proposed method [Physical Review B 96, 245131; 2017].