Théorique, numérique
This project is focused on correlated insulators of heavy elements exhibiting unusual low-temperature ordered phases. Their (Mott) insulating behavior due to narrow bandwidths and strong onsite Coulomb repulsions of their partially filled d or f bands. The large spin-orbit coupling in heavy (4d or 5d) transition-metal, lanthanide and actinide ions entangles their orbital and spin moments. In result, at low temperature such materials may host unusual phases due to ordering of high-rank ionic moments of the charge or magnetic density, i.e., multipole moments. Multiple competing order parameters and coupling mechanisms render their theoretical description challenging; predictive material-specific approaches are still lacking at present. We employ first-principles methodology to evaluate exchange interactions between multipolar moments. Other type of interaction, of an electron-lattice type, are also going to be evaluated in an ab initio way to construct many-body quantum Hamiltonians. They will be subsequently solved to obtain low-temperature ordered phases and their experimentally measurable response functions. The Master project will be focused on implementing a general approach for solving low-energy Hamiltonians within a mean-field approximation. The resulting software package will be able to treat both exchange and electron-lattice coupling on the equal footing.