Investigation of Herzberg–Teller Franck–Condon approaches and classical simulations to include effects due to vibronic coupling in circular dichroism spectra: The case of dimethyloxirane continued
Bibliographic record
Abstract
Abstract A recent study has shown that the inclusion of vibrational effects may be vital in first‐principles simulations of circular dichroism (CD) spectra. In the present work, we show that effects from vibronic coupling or, alternatively, Herzberg–Teller corrections, can have additional and perhaps unusually strong effects, due to delicate cancellations between positive and negative contributions in a CD spectrum. As full vibronic coupling simulations tend to be too demanding computationally for the sizeable molecules considered in CD spectroscopy, it is pertinent to investigate suitable approximations. In the first part of this study, we examine various Herzberg–Teller Franck–Condon (HT–FC) approaches that include the geometrical dependence of the rotatory strength for a 3 × 3 linear vibronic model, for which exact numerical results are easily obtained. Somewhat disappointingly, none of the HT–FC approaches investigated here yielded sufficiently satisfactory results. In a subsequent part of this study, we show that purely classical simulations, based on a vibronic model, can provide reliable spectra and appear to be well suited to address the dependence of the rotatory strength on nuclear geometry. From the classical simulations we extract average rotatory strengths for each electronic state, which are then used in subsequent gradient FC calculations to incorporate vibrational fine structure in the CD spectrum. This mixed classical/gradient FC approach is applied to the methyloxirane CD spectrum, using the statistical averaging of (model) orbital potentials–time‐dependent density functional theory (SAOP–TDDFT) vibronic model presented recently and is shown to improve substantially on the original simulation, corroborating the potential importance of vibronic coupling effects in simulations of CD spectra. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| 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".