CaF
CaF is a metastable, metallic compound of calcium and fluorine that serves as a subject of extensive structural research.
About CaF
CaF is a metallic compound composed of calcium and fluorine. Despite the prevalence of its more stable fluoride counterparts, this specific stoichiometry represents a unique electronic state that deviates from typical insulating behavior found in alkaline earth halides.
Due to its position above the thermodynamic hull, this material is considered metastable, making it a subject of significant interest in computational materials science. Its structural complexity is highlighted by the extensive number of configurations reported across various databases, reflecting the diverse ways these elements can arrange under different conditions.
Key Properties
Cross-validated computational properties for CaF, aggregated across 4 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.
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.
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.
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of CaF. 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.
Hull SpreadDifference between the highest and lowest energy-above-hull values reported by comparable sources. Smaller spread means less thermodynamic disagreement.
Sources ComparedNumber and names of computational sources with comparable entries for this formula.
Space Group ConsensusWhether independent sources predict the same crystal symmetry for the lowest-energy structure.
Reported Structures
Lowest-energy structures reported for CaF, 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. |
|---|---|---|---|---|---|
| C2 (No. 5) | monoclinic | 0.00 | 0.3410 | -2.792 | — |
| P63mc (No. 186) | hexagonal | 0.00 | 0.3655 | -4.761 | 2.25 |
| — | — | 0.00 | 0.3755 | -2.789 | — |
| — | — | 0.00 | 0.6641 | -2.500 | — |
| — | — | 0.00 | 0.6728 | -2.492 | — |
| — | — | 0.00 | 0.7057 | -2.459 | — |
| — | — | 0.00 | 1.1060 | -2.059 | — |
| — | — | 0.00 | 1.2478 | -1.917 | — |
| P1 (No. 1) | triclinic | — | — | — | 2.72 |
| P1 (No. 1) | triclinic | — | — | — | 1.67 |
| P1 (No. 1) | triclinic | — | — | — | 3.34 |
| P1 (No. 1) | triclinic | — | — | — | 1.98 |
Applications
Where CaF is used.
Frequently Asked Questions
Common questions about CaF, answered from cross-validated data.
What is CaF?
CaF is a metastable, metallic compound of calcium and fluorine that serves as a subject of extensive structural research.
What is CaF used for?
What is the band gap of CaF?
Is CaF a metal, semiconductor, or insulator?
Is CaF thermodynamically stable?
What is the crystal structure of CaF?
What is the density of CaF?
How many polymorphs of CaF are known?
What elements does CaF contain?
Where does the data for CaF come from?
How It Compares
As a metallic phase in a class typically dominated by insulating halides, CaF stands apart as a rare example of non-traditional bonding for these elements, serving as a critical case study for understanding the limits of stability in simple binary systems.
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)
- materials_project — Data from the Materials Project (materialsproject.org). Cite: Jain et al., APL Materials 1, 011002 (2013). (CC-BY-4.0)
- 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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