Search for negative {ital U} in the Ba{sub 1{minus}{ital x}}K{sub {ital x}}Bi{sub 1{minus}{ital y}}Pb{sub {ital y}}O{sub 3} system using constrained density-functional theory
- Institut fuer Physik, Universitaet Dortmund, 44221 Dortmund (Federal Republic of Germany)
Calculations using constrained density-functional theory have been carried out for the Ba{sub 1{minus}{ital x}}K{sub {ital x}}Bi{sub 1{minus}{ital y}}Pb{sub {ital y}}O{sub 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 {ital 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{sub 3} interaction parameters are obtained for the following models: (i) {ital s} and {ital p} orbitals at Bi and {ital p} orbitals at O sites. Here, {ital U}{sub {ital s}}=3.1{plus_minus}0.4 eV, {ital U}{sub {ital sp}}=1.4{plus_minus}0.2 eV, {ital U}{sub {ital p}}=2.2{plus_minus}0.4 eV are found, (ii) {ital s}(Bi) and {ital p}(O) orbitals, yielding {ital U}{sub {ital s}}=1.9{plus_minus}0.7 eV, and (iii) an effective one-band model, leading to {ital U}{sub {ital s}}=0.6{plus_minus}0.4 eV. Further studies have been performed for breathing distorted BaBiO{sub 3} and for various Ba{sub 1{minus}{ital x}}K{sub {ital x}}Bi{sub 1{minus}{ital y}}Pb{sub {ital y}}O{sub 3} alloys using virtual crystal approximations. The resulting {ital U} values are somewhat larger than for pure BaBiO{sub 3}. Thus, in all cases, the values of Bi {ital U} parameters are found to be positive. There is no indication of a negative {ital U} of electronic origin. {copyright} {ital 1996 The American Physical Society.}
- OSTI ID:
- 383540
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 54, Issue 9; Other Information: PBD: Sep 1996
- Country of Publication:
- United States
- Language:
- English
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