REVIEW 4 major objections 4 minor 10 references
Beyond Janus Atomic Ordering: High-Throughput First-Principles Search for Hidden MoSO Monolayer Structures
T0 review · 4 major / 4 minor · reviewed 2026-08-01 · deepseek-v4-flash
Pith's one-line read A high-throughput first-principles search of 1,325 candidate structures finds three stable non-Janus MoSO monolayers, including a metallic phase that is almost thermoneutral for hydrogen evolution.
desk verdict Three genuinely new non-Janus MoSO phases and a clear screening pipeline, but the energetic stability claim skips the convex hull and is therefore not yet established. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central mechanism is a high-throughput filtering pipeline: random sampling constrained by graph and group theory generates 1,325 MoSO monolayer arrangements, and each is passed through four DFT-based stability filters—binding energy (energetic), phonon spectra (dynamic), elastic constants (mechanical), and finite-temperature AIMD (thermodynamic)—to isolate the survivors. The 'non-Janus' label refers to monolayers in which S and O do not simply occupy the two faces; instead O and S mix within each face in periodic alternating or hybrid patterns, as in the Reversed 2H and Hybrid 2H/1T' phases.
What would settle it
Re-rank the three phases and all known Janus phases with a more accurate electronic-structure method—for example, hybrid functionals or the random-phase approximation—and run an independent evolutionary/group-theory search on a larger candidate set. If any unreported structure becomes lower in energy than the three new phases, or if the semiconducting-versus-metallic assignment of Hybrid 1T' reverses, the paper's specific conclusions fail.
Extended reading notes
Core claim
The paper's central claim is that stable non-Janus atomic arrangements of monolayer MoSO exist and have been hiding next to the well-studied Janus phase. From 1,325 candidates generated by random sampling plus graph/group theory, it distills three phases with binding energies of −4.38 to −4.51 eV/atom, all lower than Janus MoSO. Reversed 2H-MoSO and Hybrid 2H-MoSO are indirect-gap semiconductors with gaps of 1.14 eV and 1.23 eV; Hybrid 1T'-MoSO is metallic, showing band crossings near the Y point. Phonon spectra, elastic constants, and AIMD up to 2,000–2,700 K support stability. The same phase can be driven among semiconducting, semimetallic, and metallic states by biaxial strain or by rolli
Load-bearing premise
The screen's completeness and the density-functional ranking are the load-bearing premises: if the 1,325 candidates missed a lower-energy MoSO arrangement, or if the exchange-correlation approximation mis-ranks the phases, the specific list of stable non-Janus structures and their semiconducting/metallic assignments would change.
Editorial extensions
If this is right
- The family of stable 2D MoSO structures is larger than the Janus subclass; Reversed 2H, Hybrid 2H, and Hybrid 1T' are candidate targets for experimental growth by incomplete sulfidation of MoO3.
- Hybrid 1T'-MoSO is a metallic monolayer with near-zero hydrogen adsorption free energy at an O site and 0.09 eV at an S site, so it is a concrete electrocatalyst candidate.
- Applying biaxial strain between about 4 and 10 percent switches Reversed 2H and Hybrid 2H from semiconductors through semimetals to metals, and compression shifts metallic Hybrid 1T' into a semimetallic state; the same can be accomplished by choosing nanotube radius.
- The screening pipeline itself—random sampling with graph/group theory plus DFT stability filters—is a transferable method for finding hidden stable phases in other ternary 2D compounds.
Reading between the lines
- The three identified phases are a lower bound on structural diversity: because the 1,325-candidate set is stochastic, a more exhaustive search or an evolutionary algorithm could uncover additional non-Janus MoSO phases with comparable or lower energy.
- The near-zero ΔGH* at an oxygen site of a metallic monolayer suggests that the catalytic site is tied to Mo–O bonding; this points to a design rule for other MoXY oxysulfide monolayers—tune the O/S in-plane ordering rather than just the face chemistry.
- The metallic phase reported here should be testable by scanning tunneling spectroscopy; a clear zero-bias conductance peak would confirm the predicted band crossings.
- Because the band gaps are computed with a semilocal approximation, the reported 1.14 and 1.23 eV gaps are likely underestimates; the semimetal transitions at large strain may shift in quantitative terms under hybrid or GW corrections, though the qualitative ordering likely survives.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper reports a high-throughput first-principles search over 1,325 candidate MoSO monolayers, generated with a stochastic group/graph-theory approach (RG2) and relaxed with PBE-DFT. From this set, the authors identify three non-Janus structures — Reversed 2H, Hybrid 2H, and Hybrid 1T' — and claim that they are energetically, dynamically, mechanically, and thermally stable. They further report that two are indirect-gap semiconductors while Hybrid 1T' is metallic, that strain and curvature can drive semiconductor–semimetal–metal transitions, and that Hybrid 1T' has a nearly ideal HER free energy (ΔG_H* = −0.002 eV). The conclusions are presented as expanding the known MoSO structural space beyond Janus ordering.
Significance. If the stability and electronic-structure claims are correct, the work would broaden the 2D MoSO family with three previously unreported phases, and the metallic Hybrid 1T' phase would be a genuinely new electronic member with potential catalytic relevance. The high-throughput enumeration of 1,325 candidates is a useful contribution, and the combination of four stability probes is a reasonable screening protocol. The paper's value is, however, contingent on the thermodynamic stability evidence: without a convex-hull analysis against known Mo–S–O compounds, the central claim of energetic stability is incomplete. The HER and electronic-structure results are also not yet benchmarked to the level needed for quantitative predictions. With the requested additions, the manuscript could provide a solid computational discovery result.
major comments (4)
- [§III, Fig. 1(b) and binding-energy formula] The energetic stability claim rests on E_bind relative to isolated Mo, S, and O2 atoms, not on formation energies relative to competing phases. A structure with a negative E_bind can still be thermodynamically unstable with respect to decomposition into known compounds such as MoS2, MoO2, or MoO3. The manuscript never constructs a convex hull or reports distances-to-hull for the 1,325 candidates or the three finalists. This is load-bearing for the abstract and §IV claims of 'energetically stable.' Please provide hull distances computed with the same PBE settings, or explicitly rephrase the claim to 'locally stable/metastable.'
- [§III, Fig. 6 and HER discussion] The HER free energies are presented without the defining formula. The reader cannot reproduce ΔG_H* = −0.002 eV or assess whether zero-point energy and entropy corrections were included, how the computational hydrogen electrode was applied, or how the adsorption energy was referenced. Please give the explicit expression (e.g., ΔG_H* = ΔE_ad + ΔZPE − TΔS + corrections) and the numerical values for each term for the Mo, O, and S sites in the 3×2×1 supercell.
- [§II and §III, phonon dispersion (Fig. 2)] Phonon spectra are shown only along the Γ–X–S–Y–Γ path, yet the text states the structures are free of imaginary frequencies 'across the entire Brillouin zone.' A high-symmetry path can miss instabilities elsewhere. Please report phonon DOS arising from a full BZ integration, or restrict the claim to the computed path. This matters because dynamical stability is one of the four pillars of the stability claim.
- [§II, computational methodology] No convergence tests are reported for the 600 eV cutoff or the k-point sampling, and all energetics and electronic structures are at GGA-PBE without van der Waals or hybrid corrections. For 2D materials, relative phase stability can be sensitive to vdW treatment, and PBE band gaps are not quantitative. Please add convergence checks, and for the finalists report at least one higher-level comparison (e.g., DFT-D3 or HSE06 for band ordering and gaps). This is not meant to demand exhaustive benchmarks, but it is needed to support the quantitative claims (e.g., the semimetal/metallic boundaries in Fig. 4).
minor comments (4)
- [General] The manuscript text contains numerous formatting artifacts: garbled equations (e.g., the E_bind formula and Young's modulus/Poisson ratio expressions), an isolated 's' after the vacuum-layer sentence, and a 'Notions' caption in Fig. 4. These should be cleaned.
- [§III, Fig. 4] The strain maps in panels (a), (d), and (g) are described only in the text; please ensure the color scales and contour labels are legible in the final version. Also clarify what 'semimetallic' means quantitatively (band crossing vs. zero gap) in the strain regimes.
- [§III, nanotube section] The nanotube radius for Reversed 2H-MoSO is stated as 5.1 Å at which it is metallic, but the relationship between strain energy and radius is discussed qualitatively. A brief definition of the tube indices/chirality would improve reproducibility.
- [References] Reference [27] describes 1T'-MoOSe, not MoSO; this is fine as motivation, but the text should be explicit that the experimentally realized system is MoOSe, not MoSO.
Circularity Check
No circularity: the three MoSO phases are direct DFT screening outputs with no fitted parameters, and no load-bearing self-citation chain.
full rationale
The paper's derivation chain is a high-throughput structure search (RG2) followed by independent DFT evaluations. Binding energies, phonons, elastic constants, AIMD trajectories, band structures, and HER free energies are all computed from the same PBE Hamiltonian, but none of these outputs is injected back as an input or defined in terms of the target claim. E_bind is defined via total energies of isolated atoms and O2; it is a screening metric, not a fitted parameter. The selection of Reversed 2H, Hybrid 2H, and Hybrid 1T' is based on computed stability criteria, and the comparison with Janus MoSO uses DFT values from the same candidate set, so it is a comparison, not a self-fulfilling definition. The absence of a convex-hull formation-energy check and the use of PBE without vdW/hybrid corrections are accuracy/completeness concerns, not circularity. No load-bearing self-citation appears; the RG2 citation is to external prior work. No step reduces to its own input by construction.
Assumptions & free parameters
assumptions (5)
- domain assumption GGA-PBE DFT without vdW or hybrid corrections accurately predicts the relative stability and electronic phases of MoSO monolayers.
- domain assumption Phonon stability follows from absence of imaginary modes on the Γ–X–S–Y–Γ path.
- domain assumption 6 ps AIMD trajectories establish thermal stability at the reported temperatures.
- domain assumption The 1,325-candidate RG2-style search covers the relevant low-energy structural space of MoSO.
- domain assumption The HER ΔGH* values incorporate the standard computational hydrogen electrode assumptions.
Cite this review
Pith. "Pith review of Beyond Janus Atomic Ordering: High-Throughput First-Principles Search for Hidden MoSO Monolayer Structures." pith.science (2026). https://pith.science/paper/Q7AAQNX7
@misc{pith2026260716589,
author = {Pith},
title = {Pith review of: Beyond Janus Atomic Ordering: High-Throughput First-Principles Search for Hidden MoSO Monolayer Structures},
year = {2026},
howpublished = {\url{https://pith.science/paper/Q7AAQNX7}},
note = {Machine review of arXiv:2607.16589}
}
read the original abstract
Despite the growing interest in two-dimensional (2D) MoSO systems, existing studies have exclusively focused on conventional Janus structures. In this work, we perform high-throughput first-principles calculations to explore novel stable 2D MoSO monolayers. Combined with random sampling strategy, graph theory and group theory, we successfully screen out three novel non-Janus 2D MoSO monolayers from 1325 candidate structures, namely Reversed 2H-MoSO, Hybrid 2H-MoSO, and Hybrid 1T'-MoSO. Compared with Janus MoSO monolayers, the non-Janus MoSO counterparts possess lower binding energies, varying from -4.38 to -4.51 eV/atom. A systematic combination of dynamic, thermodynamic, and mechanical stability analyses corroborates their excellent structural robustness. Ab initio molecular dynamics (AIMD) simulations confirm their superior thermal resistance, with the structures remaining stable at temperatures beyond 2000 K. Interestingly, unlike the semiconducting Janus MoSO, the Hybrid 1T'-MoSO monolayer exhibits distinct metallic characteristics. Furthermore, we found that strain and curvature can enable controlled phase transitions of MoSO among semiconducting, semimetallic, and metallic phases. More importantly, the Hybrid 1T'-MoSO exhibits favorable HER activity with a Gibbs free energy of -0.002 eV, rendering it a promising candidate for hydrogen evolution catalysis. This work not only expands the family of 2D MoSO materials but also provides a reliable strategy for discovering stable functional 2D materials via high-throughput computation.
Reference graph
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Reviewed August 1, 2026 · model on record in the stance chip above.
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