Screened exchange dynamical mean-field theory and its relation to density functional theory: SrVO ₃ and SrTiO ₃

Abstract

PACS 71.15.-m -Methods of electronic structure calculations PACS 71.27.+a -Strongly correlated electron systems; heavy fermions PACS 71.10.-w -Theories and models of many-electron systems Abstract -We present the first application of a recently proposed electronic structure scheme to transition metal oxides: screened exchange dynamical mean field theory includes non-local exchange beyond the local density approximation and dynamical correlations beyond standard dynamical mean field theory. Our results for the spectral function of SrVO3 are in agreement with available experimental data, including photoemission spectroscopy and thermodynamics. Finally, the 3d 0 compound SrTiO3 serves as a test case to illustrate how the theory reduces to the band structure of standard electronic structure techniques for weakly correlated compounds.Introduction. -Combined density functional many body theories, such as the combination of the local density approximation with dynamical mean field theory ("LDA+DMFT") [1][2][3], have revolutionized the field of first principles electronic structure calculations over the last decade, and many successful applications to materials ranging from simple transition metals [4,5] or f-electron metals [6][7][8] to complex oxides [9,10] have been worked out. Nevertheless, it has also been pointed out that conceptual deficiencies related to the use of the Kohn-Sham band structure or the neglect of dynamical screening effects [11-13] may have practical implications limiting the predictive power of the approach. A more satisfactory approach, formulated entirely in a Green's function language, is the combined many-body perturbation dynamical mean field theory scheme "GW+DMFT" [14][15][16]. The first implementations of GW+DMFT have recently been elaborated, with applications to SrVO 3 [17,18] and to systems of adatoms on surfaces [19]. Nevertheless, since the approach is computationally heavy, an important line of research remains the developing and testing of approx-

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

“…This suggests the possibility of studying complex multiband materials, where a full GW +EDMFT computation would be too costly, using techniques in the spirit of the recent screened exchange + dynamical DMFT (SEx+DDMFT) method [26,27,59]. In realistic materials, the simple single-band description is not sufficient, and substantial screening effects resulting from the presence of higher-energy degrees of freedom must be taken into account [60][61][62].…”

“…The answer is based on several elements: The first point to note is that standard DFT calculations do treat exchange in a local approximation (where "local" here means again "local in the electronic structure sense"; see above), which relies on an error-cancellation effect with part of the correlation contribution (see, e.g., Ref. [26]) and is not relevant here. The next question is, therefore, Why not start from a Hartree-Fock calculation in the continuum in the full energy range of the Coulomb Hamiltonian?…”

Towards ab initio Calculations with the Dynamical Vertex Approximation

“…31) While initially thought to be well-described by now standard (back then: pioneering) DFT+DMFT calculations, 116,119,126) new aspects have been unraveled by recent advancements in, both, many-body electronic structure theory, 48,[127][128][129] and experimental techniques: 130,131) Calculations taking into account the dynamical nature of screening by allowing for retarded interactions suggest that a substantial part of the mass renormalization in SrVO 3 is driven by plasmon excitations. 47,48,50,[127][128][129] Further, V q -mediated screened exchange contributions to the self-energy were found to be important, 48,49,128,129,132) and shown to compete with the renormalization of the quasi-particle weight. 43,128) These effects beyond DMFT were predicted to be most pronounced for unoccupied states, 128) in quantitative congruence with subsequent experiments.…”

Electronic polarons, cumulants and doubly dynamical mean field theory: Theoretical spectroscopy for correlated and less correlated materials

“…In the first attempts putting up a "LDA+U(ω)+DMFT" scheme [50,51], H 0 is given by the Kohn-Sham Hamiltonian of DFT, suitably corrected for double counting terms. More recently, in the so-called "screened exchange dynamical mean field theory" a screened exchange Hamiltonian is used as a starting point [49,48,39].…”

“…Due to the overall normalisation of the spectral function, the appearance of replicae satellites is necessarily accompanied by a transfer of spectral weight to SEx+DDMFT LDA+DMFT Figure 1: Spectral function of a low-energy (t 2g -only) screened exchange Hamiltonian within standard LDA+DMFT with U=4 eV and J=0.6 eV (red curve) and "Screened Exchange + DDMFT" ("SEx+DDMFT") (black curve). The calculation uses the same setup as in [49]. Besides the low-energy electronic structure with lower and upper Hubbard bands (at -1.5 eV and 2.0 eV respectively) and a renormalized quasi-particle peak at the Fermi level, the plasmon satellites at ± 15 eV are clearly visible when the dynamical character of the interaction is included as done in SEx+DDMFT.…”