Computational investigation of the tunability of HOMO- LUMO levels and band gaps in conducting polymers
Bibliographic record
Abstract
Conducting polymers have received a lot of attention in various fields due to their tunable properties. Density functional theory (DFT) calculations were carried out to investigate the tunable nature of band gaps and HOMO and LUMO levels of polythiophene (PTh) and polypyrrole (PPy) based conjugated polymers. A GGA functional (PBE) incorporating dispersion corrections was used with TZP or plane-wave basis sets and scalar ZORA or pseudopotentials for the relativistic effects. Molecular and periodic calculations were carried out. Two series of conjugated polymers were studied as S is replaced in PTh with O, Se, Te, and N is replaced in PPy with P, As, Sb, in the presence of Li and Cl atomic dopants. Li and Cl atoms facilitate n-type and p-type doping respectively. Narrowing band gaps or HOMO-LUMO gaps were obtained when going from O to Te in PTh analogs and P to Sb in PPy analogs. Further reduction in band gaps was observed upon doping especially in the series of PTh and analogs. The tuning of the HOMO-LUMO gap was also done by replacing the peripheral hydrogen in PTh by different electron-donating and electron-withdrawing groups. As electron-donating groups -CH3, -OCH3 and -N(CH3)2 were employed, and as electron-withdrawing groups -CHO, -COOCH3, -CN and -NO2 were used. Further, S replaced by Se in PTh (polyselenophene) and molecules containing alternating heteroatoms S-Se were also studied with these different peripheral groups. The addition of electron-donating groups results in increased HOMO and LUMO levels and the addition of electron-withdrawing groups results in decreased HOMO and LUMO levels. Planarization of the molecule was observed with electron-donating groups. By changing the heteroatom from S to Se more planarized structures were observed. The structures containing both S and Se as heteroatoms have intermediate properties. Due to the changes in both HOMO and LUMO levels, the values observed for the band gap did not follow a specific trend. This study is useful in various device applications of conjugated polymers where HOMO-LUMO levels and band gaps are of concern.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".