Molecular Dynamics Simulation Study of Ethylene Glycol, Ethylenediamine, and 2-Aminoethanol. 1. The Local Structure in Pure Liquids
Bibliographic record
Abstract
This paper describes a comparative molecular dynamics (MD) simulation study of the local structure of pure liquid ethylene glycol (EG), ethylenediamine (ED), and 2-aminoethanol (AE), which are three well-known representatives of 1,2-disubstituted ethanes. As an essential component of this investigation, 12 molecular models were constructed and their gas-phase characteristics were determined. The results obtained for the molecular geometries were compared with the most reliable experimental estimates, to test different force fields and molecular representations. Liquid-phase simulations were then performed on the more successful (OPLS-based) models. The heats of vaporization and self-diffusion coefficients were used as criteria for the final selection of molecular models to be used in our subsequent detailed structural analysis. The dihedral angle distributions were calculated and relative populations of rotational isomers, with respect to the central dihedral angle, were determined. It was confirmed that, for pure liquid EG and AE, the gauche conformation accounts for the major population of isomers, whereas ED exhibits a significant population of trans conformers. The analysis of radial distribution functions (RDFs), in conjunction with calculated numbers of nearest neighbors around the O and N atoms of the main functional groups, provided some structural insights into the hydrogen-bonding pattern of the systems studied. The number of strongly hydrogen-bonded neighboring groups was determined, and their possible positions were located by means of spatial distribution functions (SDFs). The possibility of three- and four-membered nearest-neighbor arrangements (comprised of two strong and, at most, two weak hydrogen bonds) found around O and N atoms leads to the conclusion that, in the pure liquids of EG, ED, and AE, the generalized hydrogen-bonding pattern can be described as a three-dimensional, branched network.
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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 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".