<i>Ab initio</i> thermoelectric calculations of ring-shaped bands in two-dimensional <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Bi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Te</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>,</mml:mo><mml:mspace width="0.28em"/><mml:msub><mml:mi>Bi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Se</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>, and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Sb</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Te</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>: Comparison of scattering approximations
Bibliographic record
Abstract
Materials with ring-shaped electronic bands are promising thermoelectric (TE) candidates since their unusual dispersion shape is predicted to give large power factors. In this paper, we use density functional theory to investigate single and double quintuple-layer ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3},\phantom{\rule{0.28em}{0ex}}{\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, and ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ and to compare the TE properties using three scattering approximations: constant relaxation time, constant mean free path, and scattering rates proportional to the density of states (the so-called DOS model). Focus is placed on elucidating how these particular dispersion shapes influence the TE characteristics and on understanding how each scattering model impacts TE transport. The single quintuple-layer materials possess two ring-shaped valence-band maxima that provide an abrupt increase in conducting channels, which benefits the power factor. Below the band edge a ring-shaped minimum is found to further enhance TE performance within the DOS model due to a sharp drop in the DOS and, thus, scattering. An analytic ``octic'' dispersion model, designed to capture the observed characteristics of the band structure, is introduced and shown to qualitatively reproduce the first-principles results. The double quintuple-layer materials display notably worse TE properties since their dispersions are significantly modified compared to the single quintuple-layer case and lose much of the ring-shaped character. Our analysis shows that the benefits of ring-shaped bands are sensitive to the alignment of the two ring maxima and to the degree of ring anisotropy. Moreover, the predicted TE performance can vary significantly depending on the choice of scattering approximation, which could benefit from further study to assess the accuracy of these simple scattering models.
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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 | 0.010 | 0.009 |
| Meta-epidemiology (narrow) | 0.005 | 0.010 |
| Meta-epidemiology (broad) | 0.003 | 0.010 |
| Bibliometrics | 0.003 | 0.010 |
| Science and technology studies | 0.008 | 0.009 |
| Scholarly communication | 0.006 | 0.007 |
| Open science | 0.011 | 0.010 |
| Research integrity | 0.008 | 0.009 |
| Insufficient payload (model declined to judge) | 0.657 | 0.008 |
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; both teacher heads agree on what is shown here.
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".