Non-equilibrium melting and sublimation of graphene simulated with two interatomic potentials
Bibliographic record
Abstract
The mechanisms of the sublimation of graphene at zero pressure and the condensation of carbon vapor is investigated by molecular dynamics (MD) simulations. The interatomic interactions are described by the Reactive Empirical Bond Order potential (REBO). It is found that graphene sublimates at a temperature of 5,200 K. At the onset of sublimation, defects that contain several pentagons and heptagons are formed, that are shown to evolve from double vacancies and stone wales defects. These defects consisting of pentagons and heptagons act as nucleation sites for the gaseous phase. The influence of the interatomic interactions on the sublimation process are also investigated by comparing the results using the REBO potential with the Screened Environment Dependent (SED)-REBO potential. Two-dimensional MD simulations are also performed, and it is found that graphene melts at a much higher temperature and forms many more point defects than in three dimensions. It is also observed that carbon chains make up the two-dimensional molten state. The isothermal equation of state of gaseous and liquid carbon, as well as the coexistence of the two phases is calculated at 6,000 K and up to a few GPa. The analysis shows that the material that forms immediately following the phase transformation in graphene is actually a coexistence of liquid and gaseous phases, but it is primarily two-fold coordinated, so it is mostly a gas, hence the identification of the phase transformation as sublimation. The coexistence pressure for liquid and gaseous carbon is found using the Maxwell Construction to be 0.0365 GPa at 6,000 K. It was previously believed that carbon vapor consists exclusively of carbon chains. We find that under compression, at a pressure lower than the coexistence pressure, carbon vapor develops a small amount (6 %) of sp2 bonds indicating a slight non-chain bonding character. The diffusion coefficient of this dense gas is calculated to be in between that of the liquid and gaseous phases.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.001 | 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) | 0.006 | 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".