A numerically exact calculation of vibration–rotation–tunneling levels of water dimer on a new accurate potential energy surface: Achieving sub-cm−1 accuracy from the terahertz to the infrared
Bibliographic record
Abstract
Numerically exact vibrational-rotational-tunneling (VRT) levels of (H2O)2 and (D2O)2 have been computed in full dimensionality on a new highly accurate two-body potential energy surface (PES). Inter-molecular levels are computed with a basis of products of contracted intra-molecular basis functions and inter-molecular functions that are products of Wigner functions. Intra-molecular levels are computed with a product of contracted intra-molecular basis functions and contracted inter-molecular basis functions. We use a two-body PES that is fitted using the fundamental-invariant neural network method using 740 000 ab initio points. Energies for points near the bottom of the well are computed without the frozen-core approximation. The PES has a root-mean-square fitting error of only 0.70 cm-1. All the experimental VRT fork origins and tunneling splittings in the terahertz region (up to 150 cm-1) are in excellent agreement with our calculated levels. The largest error is 0.44 cm-1 for (H2O)2 and 0.85 cm-1 for (D2O)2. The calculated levels also agree very well with the 22, of a possible 24, observed OD stretch vibration-tunneling levels of (D2O)2 [Barclay et al., J. Chem. Phys. 150, 164307 (2019) and Barclay et al., 160, 114314 (2024)], with the largest error being 0.35 cm-1. Coupling, which causes predissociation, makes OH stretch states of (H2O)2 difficult to observe and their assignment is controversial. Our calculations resolve the controversy. For the only rotationally resolved experimental OH stretch state, the as[A] "2s" state [Huang and Miller, J. Chem. Phys 91, 6613 (1989)], near 3738 cm-1, the 3 observed vibrational-tunneling levels agree with the calculated levels to within 0.35 cm-1.
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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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 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) | 0.001 | 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".