Search for negativeUin theBa1−xKx<

Abstract

Calculations using constrained density-functional theory have been carried out for the Ba 1Ϫx K x Bi 1Ϫy Pb y O 3 system, using a full-potential linearized-augmented-plane-wave method and employing fcc supercell geometries with two formula units. The results have been mapped onto Hubbard-type models in order to extract values of interaction parameters U at the Bi sites. Two different mapping procedures have been utilized. The first one is the standard method, based on the comparison of total-energy curvatures. The second method, proposed in the present work, relies on the analysis of single particle energies and yields much smaller numerical errors. For BaBiO 3 interaction parameters are obtained for the following models: ͑i͒ s and p orbitals at Bi and p orbitals at O sites. Here, U s ϭ3.1Ϯ0.4 eV, U sp ϭ1.4Ϯ0.2 eV, U p ϭ2.2Ϯ0.4 eV are found, ͑ii͒ s͑Bi͒ and p͑O͒ orbitals, yielding U s ϭ1.9Ϯ0.7 eV, and ͑iii͒ an effective one-band model, leading to U s ϭ0.6Ϯ0.4 eV. Further studies have been performed for breathing distorted BaBiO 3 and for various Ba 1Ϫx K x Bi 1Ϫy Pb y O 3 alloys using virtual crystal approximations. The resulting U values are somewhat larger than for pure BaBiO 3 . Thus, in all cases, the values of Bi U parameters are found to be positive. There is no indication of a negative U of electronic origin.

Gutzwiller-Correlated Wave Functions: Application to Ferromagnetic Nickel

“…For example, in the case of the cuprates, values U ≤ 2 eV were found for a single-band Hubbard model whereas a three-band model including the oxygen 2p states employs U dd ≈ 8 eV [41]. Similar results have been found in the case of BaBiO 3 [42]. For 3d band models, values of U = 4 .…”

Magnetic exchange couplings from constrained density functional theory: An efficient approach utilizing analytic derivatives

“…8) is a variation of KS DFT that employs tunable constraintpotentials to target higher energy states with a specific physical purpose. Over the past two and a half decades a number of interesting problems have been studied successfully using C-DFT, such as the effect of Cerium impurities, 8 long-range electron transfer, 9 Hubbard interaction parameters, 10,11 spindynamics, 12 and recently magnetic exchange couplings. [13][14][15] A formal way to introduce C-DFT is usually through the Lagrange multipliers method.…”

Topological doping of a three-dimensional Peierls system: Predicted structure of dopedBaBiO3

“…If one wants to assign the mechanism for disproportionation completely to Coulomb interactions, then the Hubbard U calculated with all atoms held stationary in cubic perovskite positions (defined as U el ) should be negative. Vielsack and Weber [16] did careful calculations of U el , finding no evidence for negative values, but instead a small positive value U el ≈ 0.6 ± 0.4eV. Therefore we shall temporarily ignore the on-site Coulomb repulsion U el .…”

“…Using the value U el ≈ 0.6±0.4eV from Vielsack and Weber [16], the onsite correction 0.07 ± 0.05eV is potentially sufficient to re-stabilize the sliced solution. Thus we can say that the best place to look for sliced structures in BaBiO 3 is in the range near 1/4 to 1/3 doping, but we cannot predict whether the sliced solution will be destroyed by disorder or Coulomb effects.…”