Evaluation of Shear-Slip Transitions in Crystalline Aspirin by Density-Functional Theory
Bibliographic record
Abstract
Crystalline aspirin has been shown to form two distinct polytypes, or polymorphs, that differ only in one unit-cell dimension. The second polytype is metastable and has been proposed to convert to the original form through a one-dimensional shear-slip mechanism. The feasibility of the {100}<001> shear-slip system, relating the two known aspirin forms, is examined computationally by the use of periodic-boundary density-functional theory (B86bPBE-XDM). A low barrier of ca. 10 kJ/mol per molecule is computed, which is estimated to be consistent with the observed interconversion rate, accounting for uncertainties in the treatment of thermal effects. The barrier is shown to increase under applied pressure, explaining previous experimental observations that compression of aspirin-II did not result in reversion to aspirin-I under the time scales considered. Finally, the advisability of using aspirin, or other compounds that form similar polytypes, as tests of computational methods for studies of polymorphism is discussed. Because of their high geometric similarity, both polytypes are predicted to be effectively degenerate regardless of the treatment of intermolecular dispersion.
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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 | 0.001 | 0.001 |
| 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 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".