| 1. |
- Casula, M., et al.
(författare)
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Low-Energy Models for Correlated Materials: Bandwidth Renormalization from Coulombic Screening
- 2012
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Ingår i: Physical Review Letters. - 1079-7114. ; 109:12
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Tidskriftsartikel (refereegranskat)abstract
- We provide a prescription for constructing Hamiltonians representing the low-energy physics of correlated electron materials with dynamically screened Coulomb interactions. The key feature is a renormalization of the hopping and hybridization parameters by the processes that lead to the dynamical screening. The renormalization is shown to be non-negligible for various classes of correlated electron materials. The bandwidth reduction effect is necessary for connecting models to materials behavior and for making quantitative predictions for low-energy properties of solids.
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| 2. |
- Christiansson, Viktor, et al.
(författare)
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Self-screening corrections beyond the random-phase approximation : Applications to band gaps of semiconductors
- 2023
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Ingår i: Physical Review B. - 2469-9950. ; 107:12
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Tidskriftsartikel (refereegranskat)abstract
- The self-screening error in the random-phase approximation and the GW approximation (GWA) is a well-known issue and has received attention in recent years with several methods for a correction being proposed. Here, we apply two of these, a self-screening and a so-called self-polarization correction scheme, to model calculations to examine their applicability. We also apply a local form of the self-screening correction to ab initio calculations of real materials. We find indications for the self-polarization scheme to be the more appropriate choice of correction for localized states, while we additionally observe that it suffers from causality violations in the strongly correlated regime. The self-screening correction, on the other hand, significantly improves the description in more delocalized states. It is found to provide a notable reduction in the remaining GWA error when calculating the band gaps of several semiconductors, indicating a physical explanation for a part of the remaining discrepancy in one-shot GW compared with experiment, while leaving the localized semicore d states mostly unaffected.
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| 3. |
- Karlsson, Krister, et al.
(författare)
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Exchange-correlation kernel in time-dependent density functional theory derived from many-body theory
- 2004
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Ingår i: International Journal of Modern Physics B. - : World Scientific. - 0217-9792. ; 18:7, s. 1055-1067
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Tidskriftsartikel (refereegranskat)abstract
- We derive a simplified Bethe–Salpeter equation for calculating optical absorption based on the assumption of a local electron–hole interaction. The original four-point equation for the kernel is reduced to a two-point one. A connection to the exchange–correlation kernel in time-dependent density functional theory can be established. The resulting fxc is found to be -W/2 where W contains only the short-range (local) part of the Coulomb screened interaction. This simple approximation was successfully applied to optical absorption spectra of some excitonic crystals, reproducing not only the continuum excitons but also the bound ones.
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| 4. |
- Miyake, T., et al.
(författare)
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Effects of momentum-dependent self-energy in the electronic structure of correlated materials
- 2013
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 87:11
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Tidskriftsartikel (refereegranskat)abstract
- We study how the k dependence in the self-energy affects the quasiparticle band structure and one-particle spectral functions. It is known that, in electron-gas-like materials, the self-energy depends significantly on k and there is a strong cancellation between the k dependence and the energy dependence of the self-energy. Analysis of the GW self-energy reveals that, even in correlated materials with narrow bands, such as SrVO3, the self-energy significantly depends on k. When the nonlocal effect is neglected, the quasiparticle band structure is over-renormalized, yielding too large mass enhancement compared to the case of k-dependent self-energy. The present result suggests that partial cancellation between the frequency dependence and the k dependence in the self-energy is important when discussing the quasiparticle band structure of correlated materials. DOI: 10.1103/PhysRevB.87.115110
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| 5. |
- Nilsson, Fredrik, et al.
(författare)
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Ab initio calculations of the Hubbard U for the early lanthanides using the constrained random-phase approximation
- 2013
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 88:12
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Tidskriftsartikel (refereegranskat)abstract
- In this work we have calculated U from first principles for the early lanthanides (Ce-Gd) using the constrained random phase approximation (cRPA). We compare the static limit of U with experimental estimations from x-ray photoemission spectroscopy (XPS) and bremsstrahlung isochromat spectroscopy (BIS) spectra and also discuss the frequency dependence of U across the series. The localized subspace is constructed using maximally localized Wannier functions (MLWFs). We discuss the choice of parameters used to construct the Wannier functions and show that in the case of Eu and Gd, where the local density approximation does not yield the correct position of the 4f bands, a physically motivated choice gives better agreement with experiment.
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| 6. |
- Nilsson, Fredrik, et al.
(författare)
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Recent progress in first-principles methods for computing the electronic structure of correlated materials
- 2018
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Ingår i: Computation. - : MDPI AG. - 2079-3197. ; 6:1
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Forskningsöversikt (refereegranskat)abstract
- Substantial progress has been achieved in the last couple of decades in computing the electronic structure of correlated materials from first principles. This progress has been driven by parallel development in theory and numerical algorithms. Theoretical development in combining ab initio approaches and many-body methods is particularly promising. A crucial role is also played by a systematic method for deriving a low-energy model, which bridges the gap between real and model systems. In this article, an overview is given tracing the development from the LDA+U to the latest progress in combining the GW method and (extended) dynamical mean-field theory (GW+EDMFT). The emphasis is on conceptual and theoretical aspects rather than technical ones.
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| 7. |
- Petocchi, Francesco, et al.
(författare)
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Normal State of Nd1-xSrxNiO2 from Self-Consistent GW+EDMFT
- 2020
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Ingår i: Physical Review X. - 2160-3308. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Superconductivity with a remarkably high Tc has recently been observed in hole-doped NdNiO2, a material that shares similarities with the high-Tc cuprates. This discovery promises new insights into the mechanism of unconventional superconductivity, but at the modeling level, there are fundamental issues that need to be resolved. While it is generally agreed that the low-energy properties of cuprates can, to a large extent, be captured by a single-band model, there has been a controversy in the recent literature about the importance of a multiband description of the nickelates. Here, we use a multisite extension of the recently developed GW+EDMFT method, which is free of adjustable parameters, to self-consistently compute the interaction parameters and electronic structure of hole-doped NdNiO2. This full ab initio simulation demonstrates the importance of a multiorbital description, even for the undoped compound, and it produces results for the resistivity and Hall conductance in qualitative agreement with experiment.
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| 8. |
- Petocchi, Francesco, et al.
(författare)
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Screening from eg states and antiferromagnetic correlations in d(1,2,3) perovskites : A GW+EDMFT investigation
- 2020
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Ingår i: Physical Review Research. - 2643-1564. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- We perform a systematic ab initio study of the electronic structure of Sr(V,Mo,Mn)O3 perovskites, using the parameter-free GW+EDMFT method. This approach self-consistently calculates effective interaction parameters, taking into account screening effects due to nonlocal charge fluctuations. Comparing the results of a three-band (t2g) description to those of a five-band (t2g+eg) model, it is shown that the eg states have little effect on the low-energy properties and the plasmonic features for the first two compounds but play a more active role in SrMnO3. In the case of SrMnO3, paramagnetic GW+EDMFT yields a metallic low-temperature solution on the verge of a Mott transition, while antiferromagnetic GW+EDMFT produces an insulating solution with the correct gap size. We discuss the possible implications of this result for the nature of the insulating state above the Néel temperature, and the reliability of the GW+EDMFT scheme.
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| 9. |
- Sakuma, Rei, et al.
(författare)
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Ab initio study of the downfolded self-energy for correlated systems: Momentum dependence and effects of dynamical screening
- 2014
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 89:23
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of strongly correlated systems is usually calculated by using an effective model Hamiltonian with a small number of states and an effective on-site interaction. The mode, however, neglects the frequency dependence of the interaction, which emerges as a result of dynamical screening processes not included in the model. The self-energy calculated in this kind of model within dynamical mean-field theory (DMFT) is usually assumed to contain on-site components only. To study the validity of model calculations for the simulation of realistic materials, we make a detailed comparison between the downfolded self-energy in a model Hamiltonian with static and dynamic on-site interaction and the full ab initio self-energy for Fe and SrVO3 within the GW approximation. We find that the model GW self-energy shows weaker k (momentum) dependence than the ab initio GW self-energy, which is attributed to the lack of the long-range interaction and of contributions from other electrons not included in the models. This weak k dependence is found to lead to an artificial narrowing of the quasiparticle band structure. Moreover, this band narrowing is stronger for the dynamic (frequency-dependent) interaction, due to a larger renormalization of the quasiparticle states. These findings indicate a crucial role of the k dependence of the self-energy and dynamical screening for the electronic structure of correlated systems. We also discuss the effects beyond the GW approximation for correlated systems by comparing the GW and DMFT results.
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| 10. |
- Sakuma, Rei, et al.
(författare)
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Electronic structure of SrVO3 within GW plus DMFT
- 2013
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 88:23
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed calculation of the electronic structure of SrVO3 based on the GW + DMFT method. We show that a proper inclusion of the frequency-dependent Hubbard U and the nonlocal self-energy via the GW approximation, as well as a careful treatment of the Fermi level, are crucial for obtaining an accurate and coherent picture of the quasiparticle band structure and satellite features of SrVO3. The GW + DMFT results for SrVO3 are not attainable within the GW approximation or the LDA + DMFT scheme. We also compare the results of GW + DMFT to DMFT calculations based on the GW quasiparticle bands.
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