Modeling of [AlO<sub>4</sub>/Li<sup>+</sup>]<sup>+</sup> paramagnetic defects in α-quartz
Bibliographic record
Abstract
Two types of [AlO4/Li+]+ paramagnetic defects in α-quartz have been detected and quantitatively characterized by previous EPR experiments but remain unclear with respect to structures and formation mechanisms. We have investigated these [AlO4/Li+]+ paramagnetic defects in α-quartz by ab initio calculations at the density functional theory (DFT) level, using 72- and 108-atom supercells and all-electron basis sets. Our results show that the Al–Li coupled substitution could give rise to three distinct paramagnetic defects, two of them having the hole located on a short-bonded O atom and one trapping the hole on a long-bonded O atom. The structural models from our calculations are [AlO4/Li+(a<)]+, [AlO4/Li+(a>)]+, and [AlO4/Li+(csmall)]+ with a<, a>, and csmall indicating the position of the Li+ ion. Our calculated hyperfine constants and nuclear quadrupole parameters are in agreement with those determined from previous EPR experiments. The present study clarifies the ambiguities related to the structural model of the [AlO4/Li]q centre, discovered and proposed by Walsby et al. (Can. J. Phys. 81, 583 (2003)), and eliminates the uncertainties related to the charge of the compensating Li ion. We also suggest an additional paramagnetic defect [AlO4/Li+(csmall)]+, with the unpaired electron located on a short-bonded O atom and the Li compensator just off the edge of the small channel. However, the structural similarities with the [AlO4/Li+(a>)]+ defect would require detection and measurement of the 17O hyperfine structure for an unequivocal EPR identification.
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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) | 0.000 | 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 | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 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".