We investigate the performance of the GW approximation by comparison to exact results for small model systems. The role of the chemical potentials in Dyson’s equation as well as the consequences of numerical resonance broadening are examined, and we show how a proper treatment can improve computational implementations of many-body perturbation theory in general. GW and exchange-only calculation...

We theoretically study ferromagnetic (FM) fluctuations in the heavily overdoped region of cuprate superconductors. To explore origin FM fluctuations, we evaluate spin susceptibilities a single-band Hubbard model within fluctuation exchange approximation. Model parameters are derived using Wannierization technique and constrained random phase approximation method based on maximally localized Wan...

First-principles studies of iron oxyfluorides in the FeF2 rutile framework (FeOxF2−x, 0 ≤ x ≤ 1) are performed using density functional theory (DFT) in the general gradient approximation (GGA) with a Hubbard U correction. Studies of O/F orderings reveal FeOF to be particularly stable compared to other FeOxF2−x (x 6= 1) structures, where FeF2–FeOF mixing is not energetically favored. The band ga...

The computation scheme merging the local density approximation and the dynamical mean-field theory (DMFT) is employed to calculate spectra both below and above the Fermi energy and spin and orbital occupations in the correlated paramagnetic metallic and Mott insulating phase of V2O3. The self-consistent DMFT equations are solved by quantum Monte Carlo simulations. Room-temperature calculations ...

The so-called local density approximation plus the multi-orbital mean-field Hubbard model (LDA+U) has been implemented within the all-electron projector augmented-wave method (PAW), and then used to compute the insulating antiferromagnetic ground state of NiO and its optical properties. The electronic and optical properties have been investigated as a function of the Coulomb repulsion parameter...

The conserving approximation scheme to many-body problems was developed by Kadanoff and Baym using the functional-derivative approach. Another approach for the Hubbard model also satisfies conservation laws, but in addition it satisfies the Pauli principle and a number of sum rules. A concise formal derivation of that approach, using functional derivatives, is given in this conference paper to ...

A local, second-order (truncated) approximation is applied to the Hubbard model in three dimensions. Lowering the temperature, at half-filling, the paramagnetic ground state becomes unstable towards the formation of a commensurate spin-density-wave (SDW) state (antiferromagnetism) and sufficiently far away from half-filling towards the formation of incommensurate SDW states. The incommensurate-...

Calculations employing the local density approximation combined with static and dynamical mean field theories (LDA+U and LDA+DMFT) indicate that the metal-insulator transition observed at 32 GPa in paramagnetic LaMnO3 at room temperature is not a Mott-Hubbard transition, but is caused by orbital splitting of the majority-spin eg bands. For LaMnO3 to be insulating at pressures below 32 GPa, both...

– The Mott-Hubbard transition is studied in the context of the two-dimensional Hubbard model. Analytical calculations show the existence of a critical value Uc of the potential strength which separates a paramagnetic metallic phase from a paramagnetic insulating phase. Calculations of the density of states and double occupancy show that the ground state in the insulating phase contains always a...

The energy spectrum of molecule C70Br10 symmetry group Cs were obtained within the Hubbard model in mean-field approximation. Using theory methods, classification states was carried out, and allowed transitions bromide fullerene determined. On basis this spectrum, an interpretation experimentally observed optical absorption bands is proposed.