Quasiparticle band structure and excitonic optical response in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">V</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:mrow></mml:math> bulk and monolayer
Bibliographic record
Abstract
The electronic band structure of ${\mathrm{V}}_{2}{\mathrm{O}}_{5}$ is calculated using an all-electron quasiparticle self-consistent (QS) $GW$ method, including electron-hole ladder diagrams in the screening of $W$, named $\mathrm{QS}G\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{W}$ and using a full-potential linearized muffin-tin-orbital basis set. The optical dielectric function calculated with the Bethe-Salpeter equation (BSE) exhibits excitons with large binding energy, consistent with spectroscopic ellipsometry data and other recent calculations using a pseudopotential plane-wave-based implementation of the many-body-perturbation theory approaches. Convergence issues are discussed. Sharp peaks in the direction perpendicular to the layers at high energy are found to be an artifact of the truncation of the numbers of bands included in the BSE calculation of the macroscopic dielectric function. The static (electronic screening only) dielectric constant ${\ensuremath{\varepsilon}}_{1}(\ensuremath{\omega}=0)$ gives indices of refraction in good agreement with experiment. The exciton wave functions are analyzed in various ways. They correspond to charge transfer excitons with the hole primarily on oxygen and electrons on vanadium, but depending on which exciton, the distribution over different oxygens changes. The dark exciton at 2.6 eV is the most localized and has the highest weight on the bridge oxygen, while the lowest bright excitons for in-plane polarizations at 3.1 eV for $\mathbf{E}\ensuremath{\parallel}\mathbf{a}$ and 3.2 eV for $\mathbf{E}\ensuremath{\parallel}\mathbf{b}$ have their higher weight on the chain and vanadyl oxygens. The exciton wave functions have a spread of about 5--15\AA{}, with asymmetric character for the electron distribution around the hole depending on which oxygen the hole is fixed at. The same method applied first to bulk layered ${\mathrm{V}}_{2}{\mathrm{O}}_{5}$ is here applied to monolayer ${\mathrm{V}}_{2}{\mathrm{O}}_{5}$. The monolayer quasiparticle gap increases inversely proportional to interlayer distance once the initial interlayer covalent couplings are removed which is thanks to the long-range nature of the self-energy and the reduced screening in a two-dimensional system. The optical gap on the other hand is relatively independent of interlayer spacing because of the compensation between the self-energy gap shift and the exciton binding energy, both of which are proportional to the screened Coulomb interaction $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{W}$. Recent experimental results on very thin layer ${\mathrm{V}}_{2}{\mathrm{O}}_{5}$ obtained by chemical exfoliation provide experimental support for an increase in gap.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.023 | 0.002 |
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".