Melting in Large Sodium Clusters: An Orbital-Free Molecular Dynamics Study
Bibliographic record
Abstract
The melting-like transition in sodium clusters Na N, with N = 55, 92, and 142, is studied by using constant-energy molecular dynamics simulations. An orbital-free version of the Car−Parrinello technique is used that scales linearly with system size, allowing for investigations of the thermal behavior of large clusters. The ground-state isomer of Na 142 (an incomplete three-shell icosahedron) melts in two steps: the first (at ∼240 K) is characterized by the high mobility of atoms located on the cluster surface, and the second, homogeneous melting (at ∼270 K) involves diffusive motion of all of the atoms across the cluster. For the case of Na 92, the icosahedral structure has a larger number of surface vacancies and melts in two well-separated steps, with surface melting at ∼130 K and homogeneous melting at ∼240 K. Na 55, a complete two-shell icosahedron, melts in a single stage at ∼190 K. Our results on homogeneous melting for Na 142 and Na 92 are in excellent agreement with recent experimental determinations of melting temperatures and latent heats. However, the experimentally observed enhancement of the melting temperature around N = 55 is not reproduced by the calculations.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| 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) | 0.001 | 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".