Title:	Strong electronic correlations and magnetism in transition metals systems
DNr:	SNIC 2015/1-183
Project Type:	SNIC Medium Compute
Principal Investigator:	Igor Dimarco <igor.dimarco@physics.uu.se>
Affiliation:	Uppsala universitet
Duration:	2015-05-29 – 2016-06-01
Classification:	10304 10407
Homepage:	http://fplmto-rspt.org/
Keywords:

Abstract

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 by means of a combination of density functional theory and dynamical mean-field theory (DFT+DMFT). We will follow three major lines of research, which will be accompanied by several technical developments. First, we will focus on the role of strong correlations on the electronic and magnetic structure of transition metal (TM) elements. There exist several problems for which the DFT+DMFT method is expected to bring significant improvements to DFT results. The first problem is determining the magneto-crystalline anisotropy of fcc Ni. Standard DFT predicts the wrong easy axis, due to the presence of a spurious hole-pocket in the Fermi surface. Another outstanding problem is the description of the unusual magnetic structure of bulk Cr. The ground state of Cr is well-established experimentally, and is given by a spin density wave. However, DFT predicts bulk Cr to be either anti-ferromagnetic or non-magnetic. Other interesting studies of bulk TM elements will be focused on the energetic landscape for constrained magnetic moments. These calculations will be performed by extending DFT+DMFT with the fixed spin-moment method. Persepective applications are many, but our first choices will be Cr, Mn, and Fe, for various crystal structures and various pressures. Our second line of research will be focused on TM surfaces. Cr (001) is the most interesting problem to address. This surface is known be ferromagnetic, but the theoretical magnetic moments are largely overestimated with respect to experimental data. Furthermore, there is a on-going debate on the nature of the narrow resonance observed experimentally just above the Fermi level. Determining if the observed feature is due to an orbital Kondo resonance or to a surface state will be the main aim of this project. Finally, our third and most demanding line of research will be focused on clusters of different size. Clusters are very interesting systems, as one can focus on the transition from the atomic limit to the bulk limit by adding one atom at the time. Clusters of TM elements, e.g. Co or Fe, are particularly challenging for theory, since no computational method is at the moment able to describe them for the whole range of sizes. We will address magnetic properties such as spin and orbital moments. DFT+DMFT simulations will be compared with more exact results by means of quantum chemistry methods, at least for the clusters of smallest size. Furthermore, similar studies will be performed for clusters of TM oxides, e.g. FeO and CoO. Here our major interest lays in determining for what size the inter-atomic exchange interactions exhibit signatures of the anti-ferromagnetic super-exchange coupling observed in the bulk. The relation between size and orbital moment will also be of crucial importance.