arXiv subjects

T. Ribic

Publications and source records attributed to T. Ribic.

3 recordsLinked to original sources

arXiv2017

Role of three-particle vertex within dual fermion calculations

We investigate the influence of self-energy diagrams beyond the two-particle vertex level within dual fermion theory. Specifically, we calculate the local three-particle vertex and construct from it selected dual fermion self-energy corrections to dynamical mean field theory. For the two-dimensional Hubbard model, the thus obtained self-energy corrections are small in the parameter space where dual fermion corrections based on the two-particle vertex only are small. However, in other parts of the parameter space, they are of a similar magnitude and qualitatively different from standard dual fermion theory. The high-frequency behaviour of the self-energy correction is - surprisingly - even dominated by corrections stemming from the three-particle vertex.

cond-mat.str-el↗

arXiv2016

Nonlocal correlations and spectral properties of the Falicov-Kimball model

We derive an analytical expression for the local two-particle vertex of the Falicov-Kimball model, including its dependence on all three frequencies, the full vertex and all reducible vertices. This allows us to calculate the self energy in diagrammatic extensions of dynamical mean field theory, specifically in the dual fermion and the one-particle irreducible approach. Non-local correlations are thence included and originate here from charge density wave fluctuations. At low temperatures and in two dimensions, they lead to a larger self energy contribution at low frequencies and a more insulating spectrum.

cond-mat.str-el↗

arXiv2014

Cubic interaction parameters for t2g Wannier orbitals

Many-body calculations for multi-orbital systems at present typically employ Slater or Kanamori interactions which implicitly assume a full rotational invariance of the orbitals, whereas the real crystal has a lower symmetry. In cubic symmetry, the low-energy $t_{2g}$ orbitals have an on-site Kanamori interaction, albeit without the constraint $U = U' + 2J$ implied by spherical symmetry ($U$: intra-orbital interaction, $U'$: inter-orbital interaction, $J$: Hund's exchange). Using maximally localized Wannier functions we show that deviations from the standard, spherically symmetric interactions are indeed significant for $5d$ orbitals ($\sim25%$ for BaOsO$_3$ ; $\sim12%$ if screening is included), but less important for $3d$ orbitals ($\sim6\%$ for SrVO$_3$; $\sim1\%$ if screened).

cond-mat.str-el↗