HI
Hydrogen iodide · Hydriodic acid
Hydrogen iodide is a stable, insulating binary compound of hydrogen and iodine widely utilized as a chemical reagent.
About Hydrogen iodide
Hydrogen iodide is a binary inorganic compound composed of hydrogen and iodine. It functions as a wide-gap insulator, exhibiting electronic characteristics typical of stable molecular halides that are well-represented in structural databases.
Due to its position near the thermodynamic hull, this compound is considered a viable and synthesizable material. Its chemical nature makes it a significant reagent in various synthetic pathways, particularly in organic chemistry and specialized industrial processes.
Key Properties
Cross-validated computational properties for Hydrogen iodide, aggregated across 6 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 HI. 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 HI, 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. |
|---|---|---|---|---|---|
| — | — | 3.32 | 0.0000 | -0.067 | — |
| — | — | 3.24 | 0.0006 | -0.066 | — |
| — | — | 3.34 | 0.0023 | -0.064 | — |
| C2/c (No. 15) | monoclinic | 4.08 | 0.0044 | -2.635 | 3.42 |
| — | — | 3.44 | 0.0360 | -0.031 | — |
| C2/c (No. 15) | monoclinic | 3.22 | 0.0651 | 0.064 | — |
| — | — | 2.33 | 0.0765 | 0.010 | — |
| — | — | 1.42 | 0.1774 | 0.111 | — |
| — | — | 0.00 | 0.2745 | 0.208 | — |
| — | — | 0.32 | 0.5949 | 0.528 | — |
| — | — | 0.00 | 0.9856 | 0.919 | — |
| — | — | 0.00 | 0.9862 | 0.920 | — |
Applications
Where Hydrogen iodide is used.
Frequently Asked Questions
Common questions about Hydrogen iodide, answered from cross-validated data.
What is HI?
Hydrogen iodide is a stable, insulating binary compound of hydrogen and iodine widely utilized as a chemical reagent.
What is HI used for?
What is the band gap of HI?
Is HI a metal, semiconductor, or insulator?
Is HI thermodynamically stable?
What is the crystal structure of HI?
What is the density of HI?
How many polymorphs of HI are known?
What elements does HI contain?
Where does the data for HI come from?
How It Compares
As a fundamental binary halide, hydrogen iodide serves as a foundational reference point for understanding the behavior of hydrogen-based acidic gases. It occupies a distinct role in chemical synthesis, providing a unique reactivity profile that differentiates it from other simple hydrogen halides.
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)
- materials_project — Data from the Materials Project (materialsproject.org). Cite: Jain et al., APL Materials 1, 011002 (2013). (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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