H2O
Water · Dihydrogen monoxide, Oxidane
Water is a stable, insulating molecular compound that acts as the essential solvent for life and a wide variety of chemical processes.
About Water
Water is a fundamental molecular compound that exists as a thermodynamically stable phase under standard conditions. As a wide-gap insulator, it plays a critical role in chemical and biological systems, serving as a universal solvent and a primary medium for chemical reactions.
With an extensive range of reported structural configurations, this compound is one of the most thoroughly studied substances in materials science. Its unique ability to form complex hydrogen-bonded networks across various phases makes it a cornerstone of physical chemistry and planetary science.
Key Properties
Cross-validated computational properties for Water, 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 H2O. 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 H2O, 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. |
|---|---|---|---|---|---|
| — | — | 5.77 | 0.0000 | -1.184 | — |
| Cmc21 (No. 36) | orthorhombic | 5.52 | 0.0000 | -5.193 | 1.04 |
| P41212 (No. 92) | tetragonal | 5.49 | 0.0000 | -0.996 | — |
| Cc (No. 9) | monoclinic | 6.13 | 0.0004 | -5.192 | 1.04 |
| P63cm (No. 185) | hexagonal | 5.54 | 0.0011 | -5.192 | 1.04 |
| — | — | 5.78 | 0.0017 | -1.182 | — |
| Cmc21 (No. 36) | orthorhombic | 5.57 | 0.0027 | -0.993 | — |
| P21 (No. 4) | monoclinic | 5.43 | 0.0028 | -0.993 | — |
| Cc (No. 9) | monoclinic | 5.50 | 0.0031 | -0.993 | — |
| P212121 (No. 19) | orthorhombic | 5.82 | 0.0049 | -0.991 | — |
| R-3 (No. 148) | trigonal | 5.44 | 0.0056 | -5.187 | 1.32 |
| P212121 (No. 19) | orthorhombic | 5.71 | 0.0062 | -0.990 | — |
Applications
Where Water is used.
Patent Landscape
16 patents reference H2O or close compositional variants.
| Patent | Title | Assignee | Granted |
|---|---|---|---|
| 6950729 | Portable fuel-cell-powered system with ultrasonic atomization of H2O by-product | — | — |
| 9631286 | High performance reversible electrochemical cell for H2O electrolysis or conversion of CO2 and H2O to fuel | — | — |
| 6259971 | Portable fuel-cell-powered system with ultrasonic atomization of H2O by-product | — | — |
| 8956154 | Method and system for energy efficient conversion of a carbon containing fuel to CO2 and H2O | — | — |
| 9458740 | Method for sequestering heavy metal particulates using H2O, CO2, O2, and a source of particulates | — | — |
| 8066968 | X-ray-induced dissociation of H2O and formation of an O2-H2 alloy at high pressure | — | — |
| 9963791 | Methods for producing combustible gas from the electrolysis of water (HTE) or co-electrolysis with H2O/CO2 in | — | — |
| 10065135 | Method for sequestering heavy metal particulates using H2O, CO2, O2, and a source of particulates | — | — |
| 10053604 | Composite material for the protection of H2O sensitive devices based on surface functionalized nanozeolites di | — | — |
| 9273570 | Methods for power generation from H2O, CO2, O2 and a carbon feed stock | — | — |
Frequently Asked Questions
Common questions about Water, answered from cross-validated data.
What is H2O?
Water is a stable, insulating molecular compound that acts as the essential solvent for life and a wide variety of chemical processes.
What is H2O used for?
What is the band gap of H2O?
Is H2O a metal, semiconductor, or insulator?
Is H2O thermodynamically stable?
How many polymorphs of H2O are known?
What elements does H2O contain?
Where does the data for H2O come from?
How It Compares
As a singular, ubiquitous substance, this compound serves as the primary reference point for all other insulating molecular systems, defining the standard for solvent behavior and structural complexity in hydrogen-bonded materials.
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)
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