First-principles study on two-dimensional correlated systems : van der Waals materials and infinite-layer nickelate superconductor

Abstract

Since density functional theory (DFT) was introduced in the 1960s, DFT-based methodologies such as local density approximation (LDA) and generalized gradient approximation (GGA) have made remarkable achievements in solid-state physics. Despite its extensive and rich success, it has been known well that LDA and GGA are not sufficient to describe the strongly correlated materials where the electrons interact strongly with each other. In this thesis, I will examine the first principles methodologies that can deal with the strongly correlated systems, and introduce the route for extending and implementing these methods. Furthermore, interesting research results obtained by applying these methods to real materials are presented. More specifically, research results on magnetic van der Waals materials and nickel-based superconductors, which have recently received a lot of attention, are presented. The results of these studies, calculated by dynamic mean-field theory combined with LDA and magnetic force theorem, not only provide new insights that are not obtained from the conventional density functional theory but also give a higher level of understanding for existing experiments.