My research activities are centred around development of theoretical methods for calculating from first-principles the electronic structure of real materials, in particular those in which electron correlations are strong. These strongly correlated materials are abundant in nature and yet accurate description of their electronic structure is elusive. These materials are characterised by the presence of 3d or 4f elements such as transition metal atoms (3d) or lanthanides (4f), whose orbitals form partially filled bands. Famous examples of these materials are the cuprates high-temperature superconductors, materials possessing colossal magneto resistance, and magnetic materials in general.
The commonly used method for computing the electronic structure is density functional theory within the local density approximation (LDA) and its variants. However, for strongly correlated materials, this conventional method has been found to fail in many cases. For example, insulators are often predicted to be metals. A successful method beyond the LDA based on the Green's function technique is the GW approximation, which has been shown to be highly accurate to describe the electronic structure of metals and semiconductors in which the valence states originate from s or p electrons. Thus, the well-known underestimation of band gaps in semiconductors is very much removed within the GW approximation. However, for strongly correlated systems, even the GW approximation is not sufficient. For these systems, a suitable method is dynamical mean-field theory (DMFT), which maps the lattice problem to an Anderson impurity problem.
DMFT has a number of shortcomings, such as the assumption of local self-energy as well as a problem of double-counting when combined with LDA. My recent research activities have been focused on combining the GW approximation and DMFT, dubbed GW+DMFT , which are expected to complement each other. This GW+DMFTmethod overcomes the shortcomings of DMFT while at the same time takes advantage of the GW approximation, making the method free from adjustable parameters. The method has been successfully applied to a number of systems resulting in new interpretation of the spectral function (density of states) in the materials studied [2,3].
(1) S. Biermann, F. Aryasetiawan, and A. Georges, Phys. Rev. Lett. 90, 86402 (2003).
(2) L. Boehnke, F. Nilsson, F. Aryasetiawan, and P. Werner, Phys. Rev. B 94, 201106(R) (2016).
(3) F. Nilsson, L. Boehnke, P. Werner, and F. Aryasetiawan, Phys. Rev. Materials 1, 043803 (2017).
Recent research outputs
Research output: Contribution to journal › Article