NMR shieldings from sum-over-states density-functional-perturbation theory: Further testing of the “Loc.3” approximation
Bibliographic record
Abstract
The development and implementation of sum-over-states density-functional-perturbation theory (SOS-DFPT) [V.G. Malkin, O.L. Malkina, M.E. Casida, and D.R. Salahub, J. Am. Chem. Soc. 116, 5898 (1994)] has allowed a significant improvement in the accuracy of nuclear magnetic resonance (NMR) chemical shift values over the Hartree–Fock approximation. Furthermore, due to its computational efficiency, SOS-DFPT has opened the way to the study of systems of increased size compared to those that may be approached by more sophisticated but also computationally more intensive methods, such as Møller–Plesset perturbation theory or coupled-cluster theory. The success of SOS-DFPT relies on the introduction of an ad hoc correction to the excitation energy that improves the calculation of the paramagnetic component of the NMR shielding tensor. The lack of a clear physical basis for this approximation has left the SOS-DFPT open to some criticism. We have shown in a previous article [E. Fadda, M.E. Casida, and D.R. Salahub, Int. J. Quantum Chem. 91, 67 (2003)] that the electric field and magnetic field responses are given by equivalent expressions within the Tamm–Dancoff approximation of time-dependent density-functional theory (TD-DFT). This provides an SOS-DFPT expression which, upon restriction to diagonal contributions, yields a new rigorous “Loc.3” approximation. In this article, we more than double our original test set of 10 molecules for C13, N15, and O17 chemical shifts to a set of 25 molecules. In addition, we compare the results of “Loc.3” SOS-DFPT with the results of promising recent functionals for DFT calculations of chemical shifts. The results show not only that the “Loc.3” approximation represents the rigorous physical connection between SOS-DFPT and TD-DFT, but also that it has very good potential for the prediction of NMR shielding constants, opening the way to further developments in DFT-based NMR parameter calculations.
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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".