Multitier self-consistent GWGW+EDMFT

We discuss a parameter-free and computationally efficient ab initio simulation approach for moderately and strongly correlated materials, the multitier self-consistent $GW$+EDMFT method. This scheme treats different degrees of freedom, such as high-energy and low-energy bands, or local and nonlocal interactions, within appropriate levels of approximation, and provides a fully self-consistent description of correlation and screening effects in the solid. The ab initio input is provided by a one-shot $G^0W^0$ calculation, while the strong-correlation effects originating from narrow bands near the Fermi level are captured by a combined $GW$ plus extended dynamical mean-field (EDMFT) treatment. We present the formalism and technical details of our implementation and discuss some general properties of the effective EDMFT impurity action. In particular, we show that the retarded impurity interactions can have non-causal features, while the physical observables, such as the screened interactions of the lattice system, remain causal. We then turn to stretched sodium as a model system to explore the performance of the multitier self-consistent $GW$+EDMFT method in situations with different degrees of correlation. While the results for the physical lattice spacing $a_0$ show that the scheme is not very accurate for electron-gas like systems, because nonlocal corrections beyond $GW$ are important, it does provide physically correct results in the intermediate correlation regime, and a Mott transition around a lattice spacing of $1.5a_0$. Remarkably, even though the Wannier functions in the stretched compound are less localized, and hence the bare interaction parameters are reduced, the self-consistently computed impurity interactions show the physically expected trend of an increasing interaction strength with increasing lattice spacing.Comment: 22 pages, 19 figure

Nonequilibrium GW+EDMFT: Antiscreening and inverted populations from nonlocal correlations

We study the dynamics of screening in photo-doped Mott insulators with long-ranged interactions using a nonequilibrium implementation of the $GW$ plus extended dynamical mean field theory ($GW$+EDMFT) formalism. Our study demonstrates that the complex interplay of the injected carriers with bosonic degrees of freedom (charge fluctuations) can result in long-lived transient states with properties that are distinctly different from those of thermal equilibrium states. Systems with strong nonlocal interactions are found to exhibit a self-sustained population inversion of the doublons and holes. This population inversion leads to low-energy antiscreening which can be detected in time-resolved electron-energy loss spectra

Formation of orbital-selective electron states in LaTiO3_3/SrTiO3_3 superlattices

The interface electronic structure of correlated LaTiO$_3$/SrTiO$_3$ superlattices is investigated by means of the charge self-consistent combination of the local density approximation (LDA) to density functional theory (DFT) with dynamical mean-field theory (DMFT). Utilizing a pseudopotential technique together with a continuous-time quantum Monte-Carlo approach, the resulting complex multiorbital electronic states are addressed in a coherent fashion beyond static mean-field. General structural relaxations are taken into account on the LDA level and cooperate with the driving forces from strong electronic correlations. This alliance leads to an Ti($3d_{xy}$) dominated low-energy quasiparticle peak and a lower Hubbard band in line with photoemission studies. Furthermore correlation effects close to the band-insulating bulk SrTiO$_3$ limit as well as the Mott-insulating bulk LaTiO$_3$ limit are studied via realistic single-layer embeddings.Comment: minor refinements, added referenc

When strong correlations become weak: Consistent merging of GWGW and DMFT

The cubic perovskite SrVO3 is generally considered to be a prototype strongly correlated metal with a characteristic three-peak structure of the d-electron spectral function, featuring a renormalized quasiparticle band in between pronounced Hubbard sidebands. Here we show that this interpretation, which has been supported by numerous “ab initio” simulations, has to be reconsidered. Using a fully self-consistent GW + extended dynamical mean-field theory calculation we find that the screening from nonlocal Coulomb interactions substantially reduces the effective local Coulomb repulsion, and at the same time leads to strong plasmonic effects. The resulting effective local interactions are too weak to produce pronounced Hubbard bands in the local spectral function, while prominent plasmon satellites appear at energies which agree with those of the experimentally observed sidebands. Our results demonstrate the important role of nonlocal interactions and dynamical screening in determining the effective interaction strength of correlated compounds

Influence of Fock exchange in combined many-body perturbation and dynamical mean field theory

In electronic systems with long-range Coulomb interaction, the nonlocal Fock- exchange term has a band-widening effect. While this effect is included in combined many-body perturbation theory and dynamical mean field theory (DMFT) schemes, it is not taken into account in standard extended DMFT (EDMFT) calculations. Here, we include this instantaneous term in both approaches and investigate its effect on the phase diagram and dynamically screened interaction. We show that the largest deviations between previously presented EDMFT and GW+EDMFT results originate from the nonlocal Fock term, and that the quantitative differences are especially large in the strong-coupling limit. Furthermore, we show that the charge-ordering phase diagram obtained in GW+EDMFT methods for moderate interaction values is very similar to the one predicted by dual-boson methods that include the fermion-boson or four-point vertex