The metal-insulator transition in correlated electron systems, where electron states transform from itinerant to localized, has been one of the central themes of condensed-matter physics for more than half a century. The persistence of this question has been a consequence both of the intricacy of the fundamental issues and the growing recognition of the complexities that arise in real materials, when strong repulsive interactions play the primary role. The initial concept of Mott was based on the relative importance of kinetic hopping (measured by the bandwidth) and onsite repulsion of electrons. Real materials, however, have many further degrees of freedom that, as is recently attracting note, give rise to a rich variety of scenarios for a 'Mott transition'. Here, we report results for the classic correlated insulator MnO that reproduce a simultaneous moment collapse, volume collapse and metallization transition near the observed pressure, and identify the mechanism as collapse of the magnetic moment due to an increase of crystal-field splitting, rather than to variation in the bandwidth.

By LDA+U method with spin-orbit coupling (LDA+U+SO) the magnetic state and electronic structure have been investigated for plutonium in δ and α phases and for Pu compounds: PuN, PuCoGa5, PuRh2, PuSi2, PuTe, and PuSb. For metallic plutonium in both phases in agreement with experiment a nonmagnetic ground state was found with Pu ions in f 6 configuration with zero values of spin, orbital, and total moments. This result is determined by a strong spin-orbit coupling in 5f shell that gives in LDA calculation a pronounced splitting of 5f states on f 5/2 and f 7/2 subbands. A Fermi level is in a pseudogap between them, so that f 5/2 subshell is already nearly completely filled with six electrons before Coulomb correlation effects were taken into account. The competition between spin-orbit coupling and exchange (Hund) interaction (favoring magnetic ground state) in 5f shell is so delicately balanced, that a small increase (less than 15%) of exchange interaction parameter value from JH = 0.48 eV obtained in constrain LDA calculation would result in a magnetic ground state with nonzero spin and orbital moment values. For Pu compounds investigated in the present work, predominantly f 6 configuration with nonzero magnetic moments was found in PuCoGa5, PuSi2, and PuTe, while PuN, PuRh2, and PuSb have f 5 configuration with sizeable magnetic moment values. Whereas pure jj coupling scheme was found to be valid for metallic plutonium, intermediate coupling scheme is needed to describe 5f shell in Pu compounds. The results of our calculations show that exchange interaction term in the Hamiltonian must be treated in a general matrix form for Pu and its compounds.

Using a combination of ab initio bandstructure methods and dynamical mean-field theory we study the single-particle spectrum of the prototypical charge-transfer insulator NiO. Good agreement with photoemission and inverse-photoemission spectra is obtained for both stoichiometric and hole-doped systems. In spite of a large Ni-d spectral weight at the top of the valence band the doped holes are found to occupy mainly the ligand p orbitals. Moreover, high hole doping leads to a significant reconstruction of the single-particle spectrum accompanied by a filling of the correlation gap.

The bandstructure of the prototypical charge-transfer insulator NiO is computed by using a combination of an ab initio bandstructure method and the dynamical mean-field theory with a quantum Monte-Carlo impurity solver. Employing a Hamiltonian which includes both Ni-d and O-p orbitals we find excellent agreement with the energy bands determined from angle-resolved photoemission spectroscopy. This solves a long-standing problem in solid state theory. Most notably we obtain the low-energy Zhang-Rice bands with strongly k-dependent orbital character discussed previously in the context of low-energy model theories.PACS numbers: 71.27.+a, 71.10.-w, 79.60.-i The quantitative explanation of the electronic structure of transition metal oxides (TMOs) and other materials with correlated electrons has been a long-standing challenge in condensed matter physics. While the basic concept explaining why materials such as NiO are insulators was formulated by Mott already a long time ago [1], the development of an appropriate, material-specific computational scheme proved to be a formidable task. The electronic structure of the late TMOs, including the cuprate superconductors, is not only affected by the electronic correlations, it is further complicated by the hybridization between the transition metal d-states and O p-bands located between the lower and upper Hubbard bands formed by the transition metal d orbitals. For such materials Zaanen, Sawatzky and Allen [2] introduced the term "charge transfer insulator", a prototypical example of which is NiO. In principle the simple crystal structure of NiO allows for a straightforward comparison between theory and experiment. However, a theoretical description of the NiO bandstructure is made difficult by the competition between the local many-body effects, due to strong Coulomb interaction between Ni d electrons, and the band dispersion, due to the lattice periodicity, both observed with the angle-resolved photoemission spectroscopy (ARPES) [3,4].In this Letter we use a combination of a conventional bandstructure approach, based on the local density approximation (LDA), and the dynamical mean-field theory (DMFT) [5,6,7] to investigate the bandstructure of NiO. No adjustable parameters enter. While the application of the LDA+DMFT [8, 9, 10] framework has proven successful for the early TMOs, the charge-transfer materials were routinely avoided due to the additional complexity arising from the presence of p-bands. In the present work the O p-orbitals and their hybridization with Ni d-orbitals are explicitly included, thus allowing for a unified description of the full spectrum. Our results reveal a non-trivial effect of the p − d hybridization in strongly correlated system studied so far only in terms of simple models [11,12,13].The application of the standard bandstructure theory to NiO is marked by a failure of LDA to produce an insulating groundstate [14]. The antiferromagnetic order within LDA [15], despite rendering NiO an insulator, does not present much of an improvement sinc...

We investigate the electronic structure of LiV2O4, for which heavy-fermion behavior has been observed in various experiments, by the combination of the local density approximation and dynamical mean field theory. To obtain results at zero temperature, we employ the projective quantum Monte Carlo method as an impurity solver. Our results show that the strongly correlated a 1g band is a lightly doped Mott insulator which, at low temperatures, shows a sharp (heavy) quasiparticle peak just above the Fermi level, which is consistent with recent photoemission experiments by Shimoyamada et al. [Phys. Rev. Lett. 96, 026403 (2006)10.1103/PhysRevLett.96.026403].