Kaolin polytypes revisited ab initio at 10 GPa
Bibliographic record
Abstract
Based on systematic ab initio exploration, we reported last year that two new interlayer translations for kaolinite, -a/3 and (a+b)/3, allowed a new family of kaolin polytypes under moderate pressure. Both translations place each silicon atom of a kaolin layer on top of a hydroxyl group from the kaolin layer below, resulting in a triangular dipyramidal fivefold coordination to all silicon atoms. The predicted -a/3 translation has since been independently observed experimentally at ~7 GPa, as kaolinite III phase, by compression of a natural kaolinite (Keokuk, Iowa). Encouraged by that verification, we extend here to the entire kaolin system both translations we had predicted for kaolinite. Based on calculated enthalpies and cell volumes for models optimized with ab initio density functional theory (DFT) calculations under pressure, we report three main results. First, we predict the existence of a kaolinite IV phase at a pressure not higher than 60 GPa and its likely crystal structure. Second, we predict three novel high-pressure crystal-structure models for nacrite, ranked by their enthalpy value, one of which is likely to be observed at about 10 GPa. Finally, three other novel and ranked highpressure crystal-structure models are reported for dickite. Our results from interpretation of ab initio DFT calculations should guide experimental studies and facilitate their interpretation
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 0.001 |
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 source (direct Gemma or distilled Codex), 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".