Hi everyone,
I’m trying to reproduce the pristine InSe monolayer calculation from a recent Ni–InSe gas sensor paper that uses DMol³ in Materials Studio. In that work they report an indirect band gap of 1.968 eV for the pristine InSe monolayer.
Using Materials Studio (DMol³) I followed their computational details as closely as I can, but I consistently obtain a band gap of about 1.847 eV for the same system. I’d be very grateful if someone could help me understand whether this ~0.12 eV difference is expected, or if I’m missing some important setting.
System and structure
- Pristine InSe monolayer
- 4×4×1 supercell (32 In + 32 Se)
- In-plane lattice: a = b = 4.07 Å (fixed)
- Vacuum along z: ≈ 20 Å
- Monolayer centered in the cell
- Charge = 0, spin-polarized (spin unrestricted)
I first perform a full geometry optimization of atomic positions (cell fixed), then run a band-structure calculation on the relaxed structure.
DMol³ settings
Setup tab (Geometry Optimization):
- Task: Geometry Optimization
- Functional: GGA–PBE
- Quality: Customized
- Use Grimme (DFT-D dispersion) checked
- Spin unrestricted checked, Use formal spin as initial checked
- Metal unchecked
- Use symmetry checked
- Charge: 0
Electronic / k-points / cutoff:
- Integration accuracy: Fine
- SCF tolerance: Fine (SCF convergence set to 1×10⁻⁶ Ha)
- Smearing: 0.005 Ha (Gaussian/Fermi)
- k-point set: Customized 7×7×1 Monkhorst–Pack
- Core treatment: DFT Semi-core Pseudopots (DSSP)
- Basis set: DNP
- Orbital cutoff radius: 5.0 Å (global)
- Screening model: None
DFT-D (Grimme) options:
- DFT-D: Grimme
- Default C₆ and R₀ for In and Se (as in the Grimme parameters)
- s₆ = 0.75, d = 20.0
I use the same electronic settings for the band-structure task.
For the band structure, I follow the standard hexagonal path Γ–M–K–Γ with special points (in fractional reciprocal coordinates):
- Γ (0, 0, 0)
- M (0, 0.5, 0)
- K (−0.3333, 0.667, 0)
- Γ (0, 0, 0)
Result
- From the band-structure plot, I get an indirect band gap ≈ 1.847 eV.
- The shape of the bands (VBM/CBM positions) looks qualitatively similar to the figure in the paper, just slightly compressed in energy.
Questions for the community
- Is a difference of ~0.12 eV (1.847 vs 1.968 eV) reasonable for DMol³ given different versions / default settings, or does it suggest I’m still missing an important parameter?
- Are there hidden defaults (integration grid, smearing scheme, SCF options, occupation method, etc.) that can noticeably affect the gap for this 2D system?
- Has anyone here successfully reproduced a band gap close to 1.968 eV for pristine InSe with DMol³? If so, could you share your key settings (especially anything beyond what I’ve listed)?
- Any advice on whether I should:
- relax the lattice as well (instead of fixing a = b = 4.07 Å), or
- increase k-point density (e.g. 9×9×1) or cutoff beyond 5.0 Å
to get closer to the reported value?
Any insight from people who regularly use DMol³ for 2D semiconductors would be really helpful. Thanks in advance!
