AlF2
AlF2 has a DFT band gap of 0.25 eV across 292 reported structures in 32 space groups; its reference structure is orthorhombic (Pmmm (No. 47)). Cross-validated across 3 computational databases.
AlF
At a glance
Key Properties
Cross-validated computational properties for AlF2, 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.
0.25 eV
Range across DFT structures · ground state: insulator
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.
0.713 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.
Unstable
2 DFT sources
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
292
3 databases, 32 space groups
Validation
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of AlF2. 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.
0.79 / 1.00
Trust tier: medium
Hull SpreadDifference between the highest and lowest energy-above-hull values reported by comparable sources. Smaller spread means less thermodynamic disagreement.
0.052 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 AlF2, 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. |
|---|---|---|---|---|---|
| Pmmm (No. 47) | orthorhombic | 0.00 | 0.7132 | -2.625 | — |
| — | — | 0.25 | 0.7647 | -2.651 | — |
| P6/mmm (No. 191) | hexagonal | 0.00 | 1.2247 | -2.113 | — |
| — | — | 0.00 | 2.5234 | -0.893 | — |
| P1 (No. 1) | triclinic | — | — | — | 3.54 |
| P1 (No. 1) | triclinic | — | — | — | 2.21 |
| P1 (No. 1) | triclinic | — | — | — | 3.12 |
| P1 (No. 1) | triclinic | — | — | — | 2.87 |
| P1 (No. 1) | triclinic | — | — | — | 2.95 |
| P1 (No. 1) | triclinic | — | — | — | 2.61 |
| P1 (No. 1) | triclinic | — | — | — | 3.19 |
| P1 (No. 1) | triclinic | — | — | — | 3.32 |
Reference
Frequently Asked Questions
Common questions about AlF2, answered from cross-validated data.
What is the band gap of AlF2?
AlF2 has a DFT-computed band gap of 0.25 eV across 292 reported structures. Standard DFT underestimates band gaps, so the measured gap is typically larger.
More questions
Is AlF2 a metal, semiconductor, or insulator?
DFT predicts a band gap of up to 0.25 eV (a semiconductor). Measured gaps are typically larger.
Is AlF2 thermodynamically stable?
AlF2 has a lowest energy above hull of 0.713 eV/atom (unstable).
What is the crystal structure of AlF2?
The reference structure of AlF2 is orthorhombic symmetry, space group Pmmm (No. 47).
How many polymorphs of AlF2 are known?
292 structures of AlF2 are reported across 3 databases, spanning 32 distinct space groups.
What elements does AlF2 contain?
AlF2 contains Al and F (2 elements).
Where does the data for AlF2 come from?
AlF2 data is cross-referenced from jarvis, oqmd, mpaloe.
Data sources & attribution
- jarvis — Data from JARVIS (jarvis.nist.gov), NIST. Cite: Choudhary et al., npj Comp. Mater. 6, 173 (2020). (LicenseRef-US-Gov-PD)
- 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)
- mpaloe — Data from MP-ALOE. Cite: Kuner et al., npj Comput. Mater. (2025), doi:10.1038/s41524-025-01834-9.
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