Hidden Thermodynamic Ground State of Calcium Diazenide
Bibliographic record
Abstract
A new member to the family of alkaline earth diazenides, calcium diazenide (CaN 2 ), was recently synthesized by a controlled decomposition of calcium azide at high-pressure/high-temperature conditions (Schneider et al. Inorg. Chem. 2012, 51, 2366–2373). Isotypic to tetragonal calcium carbide, the synthesized CaN 2 phase adopts a tI6 structure in which Ca 2+ cations and [N 2 ] 2- anions are arranged in a distorted rocksalt structure. Using an unbiased structure searching method, we investigate the energy landscape of CaN 2 at the first principles level and suggest that the tI6 structure is a metastable form of CaN 2 . A new orthorhombic oP12 structure, formed by a distorted bcc lattice of Ca 2+ cations interpenetrated by [N 2 ] 2- anions, is predicted to be the thermodynamic ground state of CaN 2 . The energy of the oP12 structure is considerably lower than that of the synthesized phase, by ∼80 meV/CaN 2, while it is also lower than the energies of the candidate structures previously considered. The oP12 structure remains as the thermodynamic ground state of CaN 2 at high pressures up to 2.9 GPa, at where it undergoes a first-order phase transition to a higher density oP12′ structure. Above 2.9 GPa, the synthesized tI6 phase becomes the thermodynamic ground state of CaN 2 . The formation of the oP12 structure is predicted to be exothermic which suggests that this structure may be synthesized in future experiments with proper experimental conditions.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".