Some open issues in correlated electron systems Original Research Article

Numerical computations and simulations are important tools in the investigation of correlated electron systems. Two examples are discussed. First, monovalent (Li+) and divalent (Zn2+) dopants in a spin liquid are treated within a t–J model. Experiments that show a similar local moment for both dopants in some underdoped cuprates find a simple explanation only if Li+ does not bind a hole in these hosts. The second example illustrates the success of the generalizations of density functional method to include onsite correlation (the so-called LDA+U method) in explaining the transition between singlet semiconducting and ferromagnetic metallic states in the isostructural transition metal compounds, FeSi and FeGe.