Molecular Dynamics Investigation of Alkali Metal Ions in Liquid and Aqueous Ammonia
Bibliographic record
Abstract
A polarizable potential model for M(+)-NH3 interactions (M(+) = Li(+), Na(+), K(+), Rb(+), Cs(+)) is optimized based on the ab initio properties of the ion-ammonia dimers calculated at the MP2 level of theory. The optimized model reproduces the ab initio binding energies of M(+)(NH3)n (n = 2-4) and M(+)(NH3)n(H2O)m (n, m = 1-3 and n + m ≤ 4) clusters and gives relative solvation free energies in liquid ammonia in good agreement with experimental data, without further adjustments. It also reproduces binding cooperativity in ion-ammonia and ion-ammonia-water clusters. The model is used in molecular dynamics simulations of isolated ions in liquid ammonia and in aqueous ammonia solutions with various ammonia molar fractions (0.0 ≤ xNH3 ≤ 1.0). Simulations in liquid ammonia show coordination numbers of 4.0 for Li(+), 5.3 for Na(+), 6.1 for K(+), 6.7 for Rb(+), and 7.7 for Cs(+), in very good agreement with available experimental results. Simulations of ions in aqueous ammonia show preferential solvation by water in their first solvation shells and preferential solvation by ammonia in their second shells. Potentials of mean force are calculated between each ion and NH3 in liquid water, and between each ion and H2O in liquid ammonia. The results suggest that, in liquid water, Li(+) and Na(+) bind NH3 in their second solvation shells only, while Cs(+) binds NH3 in its first solvation shell only (K(+) and Rb(+) ions show only weak affinity for NH3 in water). In liquid ammonia, the ions bind H2O in their first solvation shells with an affinity following the trend Li(+) > Na(+) > K(+) ≈ Rb(+) > Cs(+).
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".