SI2
SI2 has a DFT band gap of 0.63–0.99 eV across 66 reported structures in 13 space groups; its reference structure is monoclinic (C2 (No. 5)). Cross-validated across 3 computational databases.
IS
At a glance
Key Properties
Cross-validated computational properties for SI2, aggregated across 3 databases.
Band GapEnergy needed to move an electron from the valence band to the conduction band. Lower or zero values tend to behave more metallic; larger gaps are more insulating or semiconducting.
0.63–0.99 eV
Range across DFT structures · ground state: narrow gap
Energy Above HullThermodynamic distance from the most stable set of competing phases. 0 eV/atom is on the convex hull; small positive values may still be experimentally accessible.
0.000 eV/atom
Best (lowest) across sources
StabilityA plain-language summary of the best reported energy-above-hull result. It reflects whether the lowest-energy structure is on, near, or far from the stability hull.
Stable
2 DFT sources
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
66
3 databases, 13 space groups
Validation
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of SI2. Tight agreement means computed properties can be trusted without re-running calculations.
Agreement ScoreA normalized confidence score summarizing how closely independent DFT databases agree. Higher scores mean tighter cross-source agreement.
0.38 / 1.00
Trust tier: low
Hull SpreadDifference between the highest and lowest energy-above-hull values reported by comparable sources. Smaller spread means less thermodynamic disagreement.
0.154 eV
EAH spread across sources
Sources ComparedNumber and names of computational sources with comparable entries for this formula.
2
jarvis, oqmd
Space Group ConsensusWhether independent sources predict the same crystal symmetry for the lowest-energy structure.
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Crystallography
Reported Structures
Lowest-energy structures reported for SI2, ranked by energy above hull.
| Space GroupSymmetry classification of the crystal arrangement. The number is the international space-group index. | Crystal SystemBroad lattice family, such as cubic, tetragonal, monoclinic, or triclinic, derived from unit-cell symmetry. | Band Gap (eV)Electronic gap calculated for this specific reported structure, measured in electronvolts. | E above hull (eV/atom)Thermodynamic distance from the convex hull for this structure, normalized per atom. Lower is generally more stable. | E/atom (eV)Computed total energy normalized per atom. Use energy above hull, not this value alone, when comparing stability. | Density (g/cm³)Mass per relaxed crystal volume, reported in grams per cubic centimeter. |
|---|---|---|---|---|---|
| — | — | 0.64 | 0.0000 | -0.138 | — |
| C2 (No. 5) | monoclinic | 0.63 | 0.1539 | 0.148 | — |
| — | — | 0.99 | 0.1772 | 0.039 | — |
| Pm (No. 6) | monoclinic | 0.00 | 0.3166 | 0.311 | — |
| Pmmm (No. 47) | orthorhombic | 0.00 | 0.5638 | 0.558 | — |
| — | — | 0.00 | 1.1607 | 1.023 | — |
| P1 (No. 1) | triclinic | — | — | — | 4.79 |
| P1 (No. 1) | triclinic | — | — | — | 6.63 |
| P1 (No. 1) | triclinic | — | — | — | 5.07 |
| P1 (No. 1) | triclinic | — | — | — | 4.17 |
| P1 (No. 1) | triclinic | — | — | — | 3.57 |
| P-1 (No. 2) | triclinic | — | — | — | 5.09 |
Reference
Frequently Asked Questions
Common questions about SI2, answered from cross-validated data.
What is the band gap of SI2?
SI2 has a DFT-computed band gap of 0.63–0.99 eV across 66 reported structures. Standard DFT underestimates band gaps, so the measured gap is typically larger.
More questions
Is SI2 a metal, semiconductor, or insulator?
DFT predicts a band gap of up to 0.99 eV (a semiconductor). Measured gaps are typically larger.
Is SI2 thermodynamically stable?
Yes — SI2 sits on the convex hull (energy above hull 0 eV/atom), i.e. stable.
What is the crystal structure of SI2?
The reference structure of SI2 is monoclinic symmetry, space group C2 (No. 5).
How many polymorphs of SI2 are known?
66 structures of SI2 are reported across 3 databases, spanning 13 distinct space groups.
What elements does SI2 contain?
SI2 contains I and S (2 elements).
Where does the data for SI2 come from?
SI2 data is cross-referenced from oqmd, jarvis, mpaloe.
Data sources & attribution
- oqmd — Data from the OQMD (oqmd.org). Cite: Saal et al., JOM 65, 1501 (2013); Kirklin et al., npj Comp. Mater. 1, 15010 (2015). (CC-BY-4.0)
- jarvis — Data from JARVIS (jarvis.nist.gov), NIST. Cite: Choudhary et al., npj Comp. Mater. 6, 173 (2020). (LicenseRef-US-Gov-PD)
- mpaloe — Data from MP-ALOE. Cite: Kuner et al., npj Comput. Mater. (2025), doi:10.1038/s41524-025-01834-9.
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