Simulation study of N<sub>2</sub>overtone solvent shifts using improved potentials
Bibliographic record
Abstract
The solvent shifts of vibrational overtone spectra are predicted by Buckingham's theory of solvent effects on Raman and infrared spectra to be linear with the overtone number. We test this prediction for liquid N2 and dilute N2 in liquid Ar by extending the theory and by implementing the predictions using molecular dynamics simulations. Changes are made to the representations of both the intermolecular and the intramolecular parts of the total Hamiltonian. The representation of the intermolecular part is extended by including two additional terms of a Taylor series expansion in the vibrational coordinate of the intermolecular energy. We find, however, that their inclusion does not contribute significantly to the predicted overtone shifts for the systems studied here. The intramolecular potential is represented by a Morse potential in contrast to Buckingham's harmonic oscillator plus a cubic perturbation term. In our calculation the only perturbation terms of the Morse oscillator Hamiltonian are four expansion terms of the intermolecular potential in terms of the vibrational coordinate. Accordingly, the basis functions used to calculate the perturbed energy levels are Morse eigenfunctions. The simulations show that Buckingham's prediction is rather accurate for liquid N2 and dilute N2 in liquid Ar, at standard state conditions, and for liquid N2 at high-pressure high-temperature conditions. We find that for N2 there is a small negative contribution due to quantum anharmonic corrections to Buckingham's harmonic solvent induced vibrational frequency shift. We also show how equivalent theoretical results are obtained when the intramolecular potential is represented as harmonic plus anharmonic terms up to the fifth power of the vibrational coordinate (i.e. a Dunham potential), instead of a Morse potential.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".