Vanadium-Engineered Co2NiSe4 Nanomaterial: Coupled Thermoelectric, Piezoelectric, and Electronic Optimization via DFT+U for Advanced Energy Applications

Amin Ur Rahman; Ayesha Riaz; Qaiser Rafiq; Qazi Muhammad Ahkam; Rafaqat Hussain; Rajwali Khan; Sikander Azam

REVIEW 5 major objections 6 minor 15 references

Vanadium-Engineered Co2NiSe4 Nanomaterial: Coupled Thermoelectric, Piezoelectric, and Electronic Optimization via DFT+U for Advanced Energy Applications

T0 review · 5 major / 6 minor · reviewed 2026-08-15 · deepseek-v4-flash

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Pith's one-line read Vanadium doping is claimed to turn Co2NiSe4 into a high-performance thermoelectric with ZT ~1.1.

desk verdict The paper's central ZT claim is not derived anywhere in the results, and the manuscript has enough internal inconsistencies (doping concentration, copied COI statement) that it should be desk rejected. read the letter →

arxiv 2509.05266 v1 pith:PPVOPKRD submitted 2025-09-05 cond-mat.mtrl-sci physics.comp-ph

Ayesha Riaz , Sikander Azam , Qaiser Rafiq , Amin Ur Rahman , Qazi Muhammad Ahkam , Rafaqat Hussain , Rajwali Khan This is my paper · ORCID

classification cond-mat.mtrl-sciphysics.comp-ph

keywords Vanadium-dopedCo2NiSe4thermoelectricfigureofmeritDFT+Upiezoelectriccoefficientsdensitystatesoptoelectronicpropertieselasticmodulispintronicmaterials

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper tries to establish that a modest amount of vanadium, substituting for cobalt in the selenide Co2NiSe4, upgrades the material on several fronts at once. Using spin-polarized DFT+U, the authors argue that 5% V doping raises the density of states at the Fermi level, sharpens spin polarization, and improves electrical conductivity while preserving ductility and thermal stability. The flagship result is a computed thermoelectric figure of merit ZT ~1.1 at 900 K, which would put V-doped Co2NiSe4 in conversation with established mid-temperature thermoelectric materials. The same doped compound is also claimed to absorb light more broadly, respond more strongly to strain, and develop larger piezoelectric coefficients, making it a candidate platform for energy harvesting, sensing, and optoelectronic devices.

What carries the argument

The load-bearing object is the vanadium impurity d-state manifold: substituting V for Co places partially filled 3d states near the Fermi level, which raises the density of states, strengthens spin polarization, and creates local lattice distortions. These states are treated with DFT+U, applying a Hubbard U of 4 eV to the transition-metal d orbitals in spin-polarized full-potential calculations. For piezoelectric coefficients the paper uses the Berry-phase formalism, which computes electric polarization from the quantum phases of Bloch states under finite strain; for transport it uses a constant-relaxation-time Boltzmann picture, which is why the reported conductivity and electronic thermal conductivity carry relaxation-time units. Effective masses of electrons and holes are then used to explain why 5% doping improves mobility while heavier doping flattens bands and degrades transport.

What would settle it

Measure the Seebeck coefficient, electrical resistivity, and total thermal conductivity, including lattice phonons, of a real 5% V-doped Co2NiSe4 sample at 900 K; if $S^{2}\sigma T/\kappa_{\text{total}}$ is substantially below 1.1, the central thermoelectric claim is contradicted. A DFT calculation with an explicit relaxation time and a computed phonon thermal conductivity would settle the same question directly.

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Extended reading notes

Core claim

The paper's central claim is that vanadium doping is a single chemical lever that simultaneously optimizes the electronic, magnetic, thermoelectric, optical, and piezoelectric behavior of Co2NiSe4. At 5% V substitution, the authors report a Seebeck coefficient that stays positive and enhanced electrical conductivity, producing a peak power factor near room temperature and a figure of merit ZT ~1.1 at 900 K; at 10% V, the Seebeck coefficient turns negative and the piezoelectric stress coefficient grows to 2.70 C/$m^{2}$. The physical origin is said to be vanadium d-states appearing near the Fermi level, which increase carrier density, enhance spin polarization (total magnetic moment rising from 3.2 to 3.6 Bohr magnetons), and introduce local lattice distortion that boosts polarizability. The authors conclude that 5% doping is the best balance for thermoelectric and optical use, while 10% doping maximizes piezoelectric response.

Load-bearing premise

The headline ZT assumes that the Seebeck coefficient, electrical conductivity, and electronic thermal conductivity, which are computed on different relaxation-time scales, can be combined into a real efficiency even though no scattering time and no lattice contribution to the thermal conductivity are provided.

Editorial extensions

If this is right

At 5% V doping, Co2NiSe4 would become a competitive mid-temperature thermoelectric, with ZT ~1.1 at 900 K and a power-factor peak already near room temperature.
The enhanced magnetic moment and spin polarization make the doped compound a candidate for spintronic and magnetic-sensor applications.
Piezoelectric coefficients of 1.90 C/m^2 at 5% V and 2.70 C/m^2 at 10% V suggest use in nanoscale electromechanical energy harvesters and actuators.
Improved bulk, shear, and Young's moduli, without losing ductility, point toward battery-electrode and flexible-device applications.
Broader optical absorption and a higher dielectric response support photodetector, infrared-sensor, and solar-conversion applications.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

The constant-relaxation-time formulation means the ZT value is not directly comparable to measured thermoelectrics; a realistic scattering time and the lattice contribution to thermal conductivity are missing, so the true optimum doping could differ from 5%.
Because 10% V flips the Seebeck sign while 5% V improves it, the optimal 5% doping looks like a carrier-concentration sweet spot; other 3d substitutions that donate similar electron counts may show the same trade-off.
The strain-induced local symmetry breaking behind the piezoelectric gain could also create a piezotronic coupling, in which mechanical strain tunes electronic transport; the paper does not explore that connection.
A direct extension would be to compute or measure the lattice thermal conductivity: if low, nanostructuring the 5% doped compound could push ZT well above 1.1.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Quick take: the headline ZT ~1.1 at 900 K never appears in the results section. Section 3.6 reports S, σ·τ, κ·τ, and PF, but no relaxation time, no lattice thermal conductivity, and no ZT. The abstract and conclusion repeat the number but the paper doesn't derive it. That alone is enough to reject the manuscript in its current form.

Credit where due: the composition is new — first DFT+U look at V-doped Co2NiSe4 — and the authors do survey a wide property set (electronic, magnetic, thermodynamic, mechanical, optical, piezoelectric). The DOS and effective-mass discussion is plausible, and the observation that 5% V gives a favorable balance of light electrons and heavier holes is a reasonable qualitative story. The elastic constants and piezoelectric coefficients are presented with tables.

But the soft spots are major and not minor. First, the doping concentration is inconsistent: the methodology says V substitutes 0.25 Co (12.5%) but all results are for 5% and 10%. No one can tell which structure produced the transport data. Second, the thermoelectric section never defines the total κ: they show only electronic κ·τ, and the text explicitly says phonon scattering is not critically important while the abstract claims 'inhibited thermal conductivity.' That is an internal contradiction. Third, there are duplicated/mislabeled figures: Fig. 3 captioned 'Density of States' for thermodynamic plots, Fig. 5 for thermoelectric, and Fig. 7 captioned 'dielectric function' for a figure that shows reflectivity/loss. Fourth, the conflict-of-interest statement is copied verbatim from a different paper about EuXO3 perovskites. That is a red flag the editor must not ignore.

The stress-test note is correct: ZT cannot be recomputed from the paper's own data. The paper even writes 'PF = S2σ/τ' in places, which is dimensionally wrong. The unit combinations in Table 5 are also suspect.

For whom is this paper? A reader wanting a qualitative survey of V-doped Co2NiSe4 might skim it, but the quantitative claims are not trustworthy. It should not receive a serious referee pass in its current form; it needs a major rewrite — rerunning calculations at a single consistent doping, reporting κ_l and τ, computing ZT explicitly, and cleaning up the copied statements.

Recommendation: desk reject.

Referee Report

5 major / 6 minor

Summary. The manuscript reports a DFT+U study of pristine and vanadium-doped Co2NiSe4, covering structural, electronic, magnetic, thermodynamic, mechanical, thermoelectric, optical, and piezoelectric properties. The central claim, repeated in the abstract, cover letter, highlights, and conclusion, is that 5 at.% V doping yields a thermoelectric figure of merit ZT ~1.1 at 900 K, alongside improved magnetic moments, elastic moduli, optical absorption, and piezoelectric coefficients. The results sections provide phonon dispersions, magnetic moments, thermodynamic curves, elastic constants, density of states, effective masses, transport coefficients, optical spectra, and piezoelectric tensors for pristine and V-doped systems.

Significance. If the headline result were reproducible, V-doped Co2NiSe4 would be a competitive mid-temperature thermoelectric and a genuinely multifunctional platform, and the breadth of computed properties would be of interest to the energy-materials community. The paper has positive features: it reports explicit tables for magnetic moments, elastic constants, effective masses, optical features, and piezoelectric coefficients, and it includes a dynamical stability check via phonon dispersion. However, the central quantitative claim, ZT ~1.1 at 900 K, is not derivable from the data presented in the manuscript: no ZT value appears in the results, no relaxation time is specified, the thermal conductivity is electronic only, and the power factor is defined with an incorrect division by the relaxation time. In addition, the doping concentration is inconsistent between the methodology (12.5%) and the property calculations (5% and 10%). These are load-bearing inconsistencies that prevent verification of the paper's main conclusion.

major comments (5)

[§3.6 and Table 5] The abstract, cover letter, highlights, and conclusion claim a peak ZT of ~1.1 at 900 K for 5% V doping, but Section 3.6 contains no calculation or table entry for ZT. Table 5 reports only κ, σ·τ, S, and PF; no relaxation time τ is given anywhere, and the thermal conductivity listed is described as electronic (κ_e). Since ZT = S²σT/(κ_e + κ_l), the reported quantities are insufficient to produce the claimed figure of merit. The abstract's headline value is therefore an unsupported assertion rather than a derived result.
[§2 and §§3.3–3.6] The methodology states that V substitutes 0.25 Co in the monoclinic unit cell, corresponding to a 12.5 at.% doping level, yet the thermodynamic, DOS, effective-mass, and thermoelectric analyses are presented for 5% and 10% V doping. The manuscript never states which structure produced the transport data in Section 3.6. Because the claimed optimal composition is the basis of the headline result, this ambiguity is not cosmetic: the 5% V thermoelectric data cannot be assigned to a well-defined supercell or doping concentration.
[§3.6, thermal conductivity paragraph] The text states that V doping produces a 'slightly positive effect on κ' and that 'phonon scattering is not critically important,' which directly contradicts the abstract's claim of 'inhibited thermal conductivity.' Moreover, the plotted and tabulated κ is the electronic contribution only; without the lattice contribution κ_l, the total thermal conductivity entering ZT is unknown, even if a relaxation time were supplied.
[§3.6, power factor definition] The power factor is defined as PF = S²σ/τ in the thermoelectric section and again in the optical-properties section, but the standard definition is PF = S²σ. The extra division by τ makes the quantity in Table 5 dimensionally inconsistent with the stated units and with the physical quantity needed for ZT. This definitional error, together with the missing τ, prevents the reader from reconstructing the claimed ZT from the paper's own equations.
[§3.6, Table 5] Table 5 is not usable for verification: the column for S (V/K) appears to contain entries for κ and σ·τ rather than Seebeck values, and no complete power-factor values are legible for the three compositions at the listed temperatures. The effective-mass table is unnumbered, and the thermoelectric section refers to 'Fig. 4 (a–e)' while the corresponding figure is labeled Fig. 5. These discrepancies make it impossible to cross-check the reported trends or to locate the data behind the abstract's ZT value.

minor comments (6)

[§2] The convergence threshold is written as '10 5 Ry' but should presumably be '10⁻⁵ Ry'; the current notation is ambiguous.
[§3.2] The text contains garbled phrasing such as 'approximately 1.0 3' and 'manganite' in a context discussing Co2NiSe4, which should be corrected.
[§3.3] The thermodynamic discussion contains word-level errors such as 'exacerbation' for the behavior of the pristine compound and 'proponentially' for the doping trend; these should be revised.
[§3.7] The caption of Fig. 7 describes the panels as 'imaginary part (ε₂) and (b) real part (ε₁)' even though the section text discusses reflectivity and energy loss spectra; the caption does not match the content.
[Declarations] The Declaration of Interest Statement refers to a different manuscript ('EuXO3 (X = Tc, Mo) Perovskites'), indicating that a template from another submission was reused; this must be corrected.
[§3.6] The text refers to the 'plot of relaxation time (Fig.5b)' but no relaxation time is plotted or quantified; the label and the surrounding discussion should be aligned.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity found: the transport, elastic, optical, and piezoelectric numbers are direct DFT outputs; the unreproducible ZT~1.1 headline is a missing derivation, not a circular derivation.

full rationale

The paper's computed results follow from a stated first-principles workflow: DFT+U with a fixed Hubbard U=4 eV, relaxed monoclinic structures, k-point convergence, energy-strain elastic constants, Berry-phase piezoelectric coefficients, and band-structure-derived transport coefficients. None of these outputs is defined in terms of the headline ZT, and no fitted parameter is renamed as a prediction. The thermoelectric section reports Seebeck coefficient, sigma*tau, kappa*tau, and power factor; the abstract's 'ZT ~1.1 at 900 K' does not appear in Table 5, no relaxation time tau or lattice thermal conductivity is specified, and no ZT formula is evaluated. That makes the headline claim unreproducible and a correctness/soundness problem, but it is not an instance of circularity under the specified patterns: there is no equation showing ZT = input by construction, no fitted input called a prediction, and no load-bearing self-citation or author-imported uniqueness theorem. The adoption of U=4 eV from prior literature is an input assumption, not a fit to the target outputs, and the references are not used to force the central conclusion. The piezoelectric and elastic results are independently computed by Berry phase and strain methods, so they stand apart from any claimed thermoelectric optimization. Overall, no significant circularity is present in the derivation chain.

Assumptions & free parameters 2 free parameters · 4 assumptions · 0 invented entities

The central claims rest on an externally chosen Hubbard U, an unverified doping-concentration mapping, and a transport analysis that never explicitly computes ZT. The absence of experimental benchmarks or machine-checked proof means all quantitative conclusions depend on these unvalidated assumptions.

free parameters (2)

Hubbard U for Co, Ni, and V 3d orbitals = 4 eV
Set by hand from prior literature, not derived in this paper; it directly controls band gaps, magnetic moments, DOS, and all derived transport, optical, and piezoelectric outputs.
Relaxation time tau
Transport results are reported as sigma/tau and kappa/tau; the claimed ZT requires a value or cancellation of tau that is never specified.

assumptions (4)

domain assumption A Hubbard U of 4 eV, applied equally to Co, Ni, and V 3d states, correctly captures the electron-correlation physics of Co2NiSe4.
No experimental or higher-level theory benchmark is provided; all derived properties depend on this choice.
ad hoc to paper The simulated substitution of 0.25 Co by V corresponds to the 5 at.% V doping that the paper claims is optimal.
Methodology states 12.5% doping while the abstract and results discuss 5% and 10%; the connection is never explained.
ad hoc to paper The constant relaxation-time approximation applies, with the same relaxation time for electrical and electronic thermal transport, and lattice thermal conductivity can be neglected when computing ZT.
Section 3.6 reports only sigma/tau and kappa/tau; no justification is given for neglecting the lattice contribution, which is essential for a ZT claim at 900 K.
domain assumption Spin-orbit coupling is negligible for the magnetic and electronic properties of Co2NiSe4.
The paper states SOC was not included because it affects ions weakly, but no SOC-included calculation is provided for comparison.

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Cite this review

Pith. "Pith review of Vanadium-Engineered Co2NiSe4 Nanomaterial: Coupled Thermoelectric, Piezoelectric, and Electronic Optimization via DFT+U for Advanced Energy Applications." pith.science (2026). https://pith.science/paper/PPVOPKRD

@misc{pith2026250905266,
  author       = {Pith},
  title        = {Pith review of: Vanadium-Engineered Co2NiSe4 Nanomaterial: Coupled Thermoelectric, Piezoelectric, and Electronic Optimization via DFT+U for Advanced Energy Applications},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/PPVOPKRD}},
  note         = {Machine review of arXiv:2509.05266}
}

read the original abstract

To realize the creation of advanced multifunctional materials in energy storage and conversion technologies, the present research evaluates the structural, electronic, magnetic, thermodynamic, mechanical, thermoelectric, piezoelectric and optical properties of pristine and vanadium-doped Co2NiSe4 by first-principles density functional theory (DFT + U ). It addresses the use of vanadium substitution to tailor the material, its performance and the inclusion of diverse fields by changing its electronic structure and its bonding properties. It can be seen in the results that V doping improves electrical conductivity and magnetic ordering because of a higher density of states and a stronger spin polarization at the Fermi level. Thermodynamic calculations show enhanced entropy stabilization at high temperatures and, mechanical analysis suggests an enhanced elastic moduli that proves the enhanced structural integrity without affecting ductility. The thermoelectric properties have been greatly improved realize an optimal ZT of ~1.1 at 900 K with 5 at.% V doping owing to an ideal combination of Seebeck coefficient, electrical conductivity, and inhibited thermal conductivity. Also, optical analysis reveals that expanded absorption spectra, increased dielectric response, adjustable reflectivity and energy loss spectra, optical properties can be used in photonic, and other optoelectronic devices. Better piezoelectric coefficients due to its effectiveness when doped also appeal to the usefulness of its application in nanoscale electromechanical systems. The combination of these results makes V-doped Co2NiSe4, a versatile material platform of next-generation energy storage, thermoelectric generation, and novel multifunctional sensors.

Figures

Figures reproduced from arXiv: 2509.05266 by the authors.

**Figure 1.** A conventional unit cell for the presented Co2NiSe4 3. Results and Discussions 3.1. Vibrational properties Their phonon dispersion spectra show the vibrational character of Co2NiSe4 and Co2NiSe4: V structures as shown in [PITH_FULL_IMAGE:figures/full_fig_p014_1.png] view at source ↗

**Figure 2.** Description of the vibrational properties of Co2NiSe4 and its V-doped 3.2. Magnetic Properties The magnets behavior of Co2NiSe4 and V-doped modification should be studied in order to help understand the utility of the ingredient in most domains, especially spin-sensitive and magnetic sensors energy appliances. Answering this question, using first-principles DFT+U calculations it is possible to realize that doping wi… view at source ↗

**Figure 3.** Thermodynamic performance of the presenting material, E [PITH_FULL_IMAGE:figures/full_fig_p024_3.png] view at source ↗

Figures from the paper (2 more)

**Figure 5.** Figure 5: Calculated the dielectric function, (a) imaginary part (ε₂) and (b) real part (ε₁) for Co₂NiSe₄ and V-Doped Co₂NiSe₄ Alloys (5% and 10%) using GGA+U Reflectivity and Energy Loss Spectra of Co₂NiSe₄ and V-Doped Co₂NiSe₄ Alloys (5% and 10%) To acquire the multifunctional…

**Figure 8.** Figure 8: bar chart showing the variation of the piezoelectric stress coefficient as a function of vanadium doping concentration in Co₂NiSe₄ [PITH_FULL_IMAGE:figures/full_fig_p046_8.png]

Discussion (0). Continue with ORCID to comment.

Reference graph

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Pith tools

Reviewed August 15, 2026 · model on record in the stance chip above.

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