| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Sakuma, Rei, et al.
(författare)
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First-principles calculations of dynamical screened interactions for the transition metal oxides MO (M = Mn, Fe, Co, Ni)
- 2013
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 87:16
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Tidskriftsartikel (refereegranskat)abstract
- To facilitate reliable and accurate modeling of the late transition metal oxides from first principles, we present detailed and systematic calculations of the dynamical screened Coulomb interactions (Hubbard U) of MnO, FeO, CoO, and NiO within the constrained random-phase approximation. The matrix elements of the screened interactions are calculated in maximally localized Wannier functions. We consider the screened interactions not only for conventional models that include only the d-like bands but also for models that include both the transition metal d bands and the oxygen p bands. The screened interaction is found to be sensitive to the screening channels subtracted from the polarization function. The frequency dependence of the screened interactions of these oxides is characterized by the two sharp peaks in low-energy region that may be called "subplasmons," which arise from the particle-hole transitions between d and oxygen p states. DOI: 10.1103/PhysRevB.87.165118
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| 6. |
- Sakuma, Rei, et al.
(författare)
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Self-energy and spectral function of Ce within the GW approximation
- 2012
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 86:24
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Tidskriftsartikel (refereegranskat)abstract
- To investigate how far the GW approximation can treat systems with strong on-site correlations, we perform calculations of the self-energies and spectral functions of alpha-and gamma-Ce within the GW approximation. For this strongly correlated material, the screened interaction exhibits a complex and rich structure which is attributed to strong particle-hole transitions involving localized 4f states. This structure in the screened interaction is carried over to the self-energy, which in turn yields spectral functions with multiple peaks. A satellite at around 5 eV above the Fermi level is formed, which is reminiscent of the experimentally observed upper Hubbard band, while the experimentally observed peak structure below the Fermi level at -2 eV and disappearance of the quasiparticle peak in the. phase are not reproduced. DOI: 10.1103/PhysRevB.86.245126
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| 7. |
- Sakuma, Rei
(författare)
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Symmetry-adapted Wannier functions in the maximal localization procedure
- 2013
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 87:23
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Tidskriftsartikel (refereegranskat)abstract
- A procedure to construct symmetry-adapted Wannier functions in the framework of the maximally localized Wannier function approach [Marzari and Vanderbilt, Phys. Rev. B 56, 12847 (1997); Souza, Marzari, and Vanderbilt, ibid. 65, 035109 (2001)] is presented. In this scheme, the minimization of the spread functional of the Wannier functions is performed with constraints that are derived from symmetry properties of the specified set of the Wannier functions and the Bloch functions used to construct them, therefore one can obtain a solution that does not necessarily yield the global minimum of the spread functional. As a test of this approach, results of atom-centered Wannier functions for GaAs and Cu are presented.
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| 8. |
- Werner, Philipp, et al.
(författare)
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Dynamical screening in La2CuO4
- 2015
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 91:12
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Tidskriftsartikel (refereegranskat)abstract
- We show that the dynamical screening of the Coulomb interaction among Cu-d electrons in high-Tc cuprates is strong and that a proper treatment of this effect is essential for a consistent description of the electronic structure. In particular, we find that ab initio calculations for undoped La2CuO4 in the paramagnetic phase yield an insulator only if the frequency dependence of the Coulomb interaction and the interatomic interaction between p and d electrons are taken into account. We also identify a collective excitation in the screened interaction at 9 eV, which is rather localized on the copper site, and which is responsible for a satellite structure at energy -13 eV, located below the p bands.
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