Ca2C
Ca2C has a DFT band gap of 0.39 eV across 23 reported structures in 9 space groups; its reference structure is cubic (Fm-3m (No. 225)). Cross-validated across 3 computational databases.
CCa
At a glance
Key Properties
Cross-validated computational properties for Ca2C, 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.
0.39 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.
0.244 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.
23
3 databases, 9 space groups
Validation
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of Ca2C. 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.
0.57 / 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.
0.108 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.
—
Crystallography
Reported Structures
Lowest-energy structures reported for Ca2C, 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. |
|---|---|---|---|---|---|
| Fm-3m (No. 225) | cubic | 0.39 | 0.2441 | 0.142 | — |
| R-3m (No. 166) | trigonal | 0.00 | 0.2867 | 0.184 | — |
| — | — | 0.00 | 0.3517 | 0.337 | — |
| — | — | 0.00 | 0.8306 | 0.816 | — |
| Cmmm (No. 65) | orthorhombic | 0.00 | 0.8747 | 0.772 | — |
| Pmmm (No. 47) | orthorhombic | 0.00 | 0.8931 | 0.791 | — |
| P4/mmm (No. 123) | tetragonal | 0.00 | 1.6846 | 1.582 | — |
| — | — | 0.00 | 2.2643 | 2.250 | — |
| P-1 (No. 2) | triclinic | — | — | — | 1.65 |
| C2/m (No. 12) | monoclinic | — | — | — | 1.89 |
| P-1 (No. 2) | triclinic | — | — | — | 1.85 |
| P-1 (No. 2) | triclinic | — | — | — | 1.68 |
Reference
Frequently Asked Questions
Common questions about Ca2C, answered from cross-validated data.
What is the band gap of Ca2C?
Ca2C has a DFT-computed band gap of 0.39 eV across 23 reported structures. Standard DFT underestimates band gaps, so the measured gap is typically larger.
More questions
Is Ca2C a metal, semiconductor, or insulator?
DFT predicts a band gap of up to 0.39 eV (a semiconductor). Measured gaps are typically larger.
Is Ca2C thermodynamically stable?
Ca2C has a lowest energy above hull of 0.244 eV/atom (unstable).
What is the crystal structure of Ca2C?
The reference structure of Ca2C is cubic symmetry, space group Fm-3m (No. 225).
How many polymorphs of Ca2C are known?
23 structures of Ca2C are reported across 3 databases, spanning 9 distinct space groups.
What elements does Ca2C contain?
Ca2C contains C and Ca (2 elements).
Where does the data for Ca2C come from?
Ca2C 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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