Hybridization effects and bond disproportionation in the bismuth perovskites
Bibliographic record
Abstract
We propose a microscopic description of the bond-disproportionated insulating state in the bismuth perovskites $X{\mathrm{BiO}}_{3}$ ($X=\text{Ba},\text{Sr}$) that recognizes the bismuth-oxygen hybridization as a dominant energy scale. It is demonstrated by using electronic structure methods that the breathing distortion is accompanied by spatial condensation of hole pairs into local, molecularlike orbitals of the ${A}_{1g}$ symmetry composed of O-$2{p}_{\ensuremath{\sigma}}$ and Bi-$6s$ atomic orbitals of collapsed ${\mathrm{BiO}}_{6}$ octahedra. The primary importance of oxygen $p$ states is thus revealed, in contrast to a popular picture of a purely ionic ${\mathrm{Bi}}^{3+}/{\mathrm{Bi}}^{5+}$ charge disproportionation. Octahedra tilting is shown to enhance the breathing instability by means of a nonuniform band narrowing. We argue that the formation of localized states upon breathing distortion is, to a large extent, a property of the oxygen sublattice, and we expect similar hybridization effects in other perovskites involving formally high oxidation state cations.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".