# Cu2O: enthalpy of formation > Enthalpy of formation of Cu2O: 8 literature value(s) with sources, pages and quotes and DFT values (Materials Project / OQMD), from ORCHID. HTML: https://data.orchid-project.org/compounds/Cu2O.html · Markdown: https://data.orchid-project.org/compounds/Cu2O.md 8 accepted literature formation-enthalpy value(s) (experimental 5, model 3); experimental median -56.943 kJ/mol-atom (n = 5); Materials Project -62.185 kJ/mol-atom (mp-aaaaaanx); OQMD -66.037 kJ/mol-atom (oqmd-643065). Systems: [Cu–O](https://data.orchid-project.org/systems/CU-O.html) ## Literature values Table: Enthalpy of formation of Cu2O reported in the literature (8) | Value | Phase as printed | T (K) | Class | Method | System | Source | Location | Quote | |---:|---|---:|---|---|---|---|---|---| | -59.97 kJ/mol-atom | Cu2O | 298.15 | experimental | Cal. | [Cu–O](https://data.orchid-project.org/systems/CU-O.html) | [1] Hallstedt 1994; _cites Wrhler 1934_ | Table 8, p. 13, row 4; `ORC-UEENQAKLM2.5a9513` | | | -57.7267 kJ/mol-atom | Cu2O | 298.15 | experimental | React. Cal. | [Cu–O](https://data.orchid-project.org/systems/CU-O.html) | [1] Hallstedt 1994; _cites Nufiez 1969_ | Table 8, p. 13, row 10; `ORC-ALFTX6OZRM.279a7f` | | | -56.9433 kJ/mol-atom | Cu2O | 298.15 | experimental | React. Cal. | [Cu–O](https://data.orchid-project.org/systems/CU-O.html) | [1] Hallstedt 1994; _cites Mah 1967_ | Table 8, p. 13, row 8; `ORC-AJGT674S4D.b11196` | | | -56.7633 kJ/mol-atom | Cu2O | 298.15 | experimental | Aq. Cal. | [Cu–O](https://data.orchid-project.org/systems/CU-O.html) | [1] Hallstedt 1994; _cites Thomsen 1883_ | Table 8, p. 13, row 1; `ORC-T4WZFE2TJJ.eef88f` | | | -54.95 kJ/mol-atom | Cu2O | 293 | experimental | Sol. Cal. | [Cu–O](https://data.orchid-project.org/systems/CU-O.html) | [1] Hallstedt 1994; _cites ref. 34Bil_ | Table 8, p. 13, row 6; `ORC-LGOKEWXJHR.56dd6b` | | | -57.4933 kJ/mol-atom | Cu2O | 298.15 | model | Assessed | [Cu–O](https://data.orchid-project.org/systems/CU-O.html) | [1] Hallstedt 1994; _cites Boud 1991_ | Table 8, p. 13, row 15; `ORC-UDWXTWFN6Y.223526` | | | -56.9033 kJ/mol-atom | Cu2O | 298.15 | model | Assessed | [Cu–O](https://data.orchid-project.org/systems/CU-O.html) | [1] Hallstedt 1994; _cites Chase 1985_ | Table 8, p. 13, row 13; `ORC-XCCWO6H7LI.d9fe69` | | | -56.7533 kJ/mol-atom | Cu2O | 298.15 | model | Assessed | [Cu–O](https://data.orchid-project.org/systems/CU-O.html) | [1] Hallstedt 1994 | Table 8, p. 13, row 17; `ORC-SNTTKLS5GR.c8b64e` | | ### Uncertainty budget Components kept separate, in the value's unit (literature [SCHEMA.md](https://data.orchid-project.org/literature/SCHEMA.md), [UNCERTAINTY_CALIBRATION.md](https://data.orchid-project.org/literature/UNCERTAINTY_CALIBRATION.md)): effective = max(sqrt(max(printed, reading, method)^2 + composition^2 + conversion^2), scatter). The method floor is the robust between-study scatter of the method class in ORCHID (calibrated) or a documented prior; printed values and printed uncertainties are unchanged. Table: Uncertainty budget of the literature values of Cu2O | Value | Unit | Printed | Reading | Method (class, basis) | Composition | Scatter | Conversion | Effective | |---:|---|---:|---:|---|---:|---:|---:|---:| | -59.97 | kJ/mol-atom | | 0.001667 | 3.2 (solution_reaction_calorimetry, calibrated) | | | | 3.2 | | -57.7267 | kJ/mol-atom | | 0.001667 | 3.2 (solution_reaction_calorimetry, calibrated) | | | | 3.2 | | -56.9433 | kJ/mol-atom | | 0.001667 | 3.2 (solution_reaction_calorimetry, calibrated) | | | | 3.2 | | -56.7633 | kJ/mol-atom | | 0.001667 | 3.2 (solution_reaction_calorimetry, calibrated) | | | | 3.2 | | -54.95 | kJ/mol-atom | | 0.001667 | 3.2 (solution_reaction_calorimetry, calibrated) | | | | 3.2 | | -57.4933 | kJ/mol-atom | | 0.001667 | 3.9 (model_calculated, calibrated) | | | | 3.9 | | -56.9033 | kJ/mol-atom | | 0.001667 | 3.9 (model_calculated, calibrated) | | | | 3.9 | | -56.7533 | kJ/mol-atom | | 0.001667 | 3.9 (model_calculated, calibrated) | | | | 3.9 | ## DFT formation energies Lowest-energy entries at this composition. Materials Project and OQMD use different energy references and are never averaged. 1 eV/atom = 96.485 kJ/mol-atom. Table: DFT formation energy of Cu2O | Source | Entry | kJ/mol-atom | eV/atom | Space group | E above hull (kJ/mol-atom) | E above hull (eV/atom) | Theoretical | |---|---|---:|---:|---|---:|---:|---| | Materials Project | mp-aaaaaanx | -62.185 | -0.644505 | Pn-3m | 0 | 0 | no | | OQMD | oqmd-643065 | -66.037 | -0.684424 | Pn-3m | 0 | 0 | no | DFT sources: A. Jain et al., Commentary: The Materials Project: A materials genome approach to accelerating materials innovation, APL Materials 1 (2013) 011002. [doi:10.1063/1.4812323](https://doi.org/10.1063/1.4812323) (CC BY 4.0); J. E. Saal et al., JOM 65 (2013) 1501-1509; S. Kirklin et al., npj Comput. Mater. 1 (2015) 15010. [doi:10.1007/s11837-013-0755-4](https://doi.org/10.1007/s11837-013-0755-4) (CC BY 4.0); ## Sources 1. B. Hallstedt, D. Risold, L. J. Gauckler, Thermodynamic assessment of the copper-oxygen system, JPE 15, 483-499 (1994). [doi:10.1007/bf02649399](https://doi.org/10.1007/bf02649399) ## Please cite - R. Arróyave, J. Saal, D. Shin, ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature (version 2026.10; Version 1, machine-extracted), Zenodo (2026). https://doi.org/10.5281/zenodo.23735569 - R. Arróyave, J. Saal, D. Shin, ORCHID-Parity: DFT-vs-experiment formation-enthalpy benchmark (version 2026.10; Version 1, machine-extracted), Zenodo (2026). https://doi.org/10.5281/zenodo.23735943 - R. Arróyave, J. Saal, D. Shin, ORCHID data: umbrella record of the ORCHID datasets (version 2026.10; Version 1, machine-extracted), Zenodo (2026). https://doi.org/10.5281/zenodo.23736065 Also cite the original source of every value you use (paper_citation / paper_doi, and cited_dois for values the paper cites from earlier work); A. Jain et al., The Materials Project: A materials genome approach to accelerating materials innovation, APL Materials 1 (2013) 011002, https://doi.org/10.1063/1.4812323 (CC BY 4.0); J. E. Saal et al., JOM 65 (2013) 1501, https://doi.org/10.1007/s11837-013-0755-4 and S. Kirklin et al., npj Comput. Mater. 1 (2015) 15010, https://doi.org/10.1038/npjcompumats.2015.10 (CC BY 4.0); G. Kim, S. V. Meschel, P. Nash, W. Chen, Experimental formation enthalpies for intermetallic phases and other inorganic compounds, Scientific Data 4 (2017) 170162, https://doi.org/10.1038/sdata.2017.162; B. Hallstedt, The SGTE collection of binary datasets, Calphad 89 (2025) 102833, https://doi.org/10.1016/j.calphad.2025.102833 (CC BY 4.0), and the original assessment named in each file. Version 1, machine-extracted: values were read by language-model readers constrained to quote their source and checked automatically, and the release was then audited on the printed pages by adversarial audits, an independent second review of fit-facing records and a preliminary human review of a frozen sample. Flags such as accepted and ESPEI-ready record screening results, not certification; known issues are listed in the release notes. ```bibtex @misc{orchid_literature_2026, author = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon}, title = {{ORCHID-Values: thermodynamic and phase-equilibrium values read from the literature}}, version = {2026.10}, publisher = {Zenodo}, year = {2026}, doi = {10.5281/zenodo.23735569}, url = {https://doi.org/10.5281/zenodo.23735569}, note = {Version 1, machine-extracted} } @misc{orchid_dft_benchmark_2026, author = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon}, title = {{ORCHID-Parity: DFT-vs-experiment formation-enthalpy benchmark}}, version = {2026.10}, publisher = {Zenodo}, year = {2026}, doi = {10.5281/zenodo.23735943}, url = {https://doi.org/10.5281/zenodo.23735943}, note = {Version 1, machine-extracted} } @misc{orchid_data_2026, author = {Arr{\'o}yave, Raymundo and Saal, James and Shin, Dongwon}, title = {{ORCHID data: umbrella record of the ORCHID datasets}}, version = {2026.10}, publisher = {Zenodo}, year = {2026}, doi = {10.5281/zenodo.23736065}, url = {https://doi.org/10.5281/zenodo.23736065}, note = {Version 1, machine-extracted} } ``` --- Derived data CC BY 4.0 ([licence](https://creativecommons.org/licenses/by/4.0/)): cite ORCHID ([CITATION.cff](https://data.orchid-project.org/CITATION.cff)) and the original sources. Quotes are short excerpts kept so that each value can be checked; they remain under the publishers' copyright and are not relicensed. Source papers, page images and full text are not redistributed. Field reference: [SCHEMA.md](https://data.orchid-project.org/literature/SCHEMA.md). Machine-readable guide: [llms.txt](https://data.orchid-project.org/llms.txt). Found an error? The report link of a value (Markdown: its id, ORC-..., in the Location column) opens a pre-filled GitHub issue, https://github.com/orchid-calphad/orchid-data/issues/new?template=report-value-error.yml&record_id=\, carrying only the record id, source and value; [how to contribute](https://orchid-project.org/contribute/).