# ONIOM

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The **ONIOM** (short for '**O**ur own **N**-layered **I**ntegrated molecular **O**rbital and **M**olecular mechanics'[1]) method is a [computational](/source/Computational_chemistry) approach developed by [Keiji Morokuma](/source/Keiji_Morokuma) and co-workers. ONIOM is a hybrid method that enables different [ab initio](/source/Ab_initio_quantum_chemistry_methods), [semi-empirical](/source/Semi-empirical_quantum_chemistry_method), or [molecular mechanics](/source/Molecular_mechanics) methods to be applied to different parts of a molecule/system in combination to produce reliable [geometry](/source/Molecular_geometry) and [energy](/source/Energy_level) at reduced computational cost.[2][3][4]

The ONIOM computational approach has been found to be particularly useful for modeling [biomolecular systems](/source/Biomolecule)[5] as well as for [transition metal complexes](/source/Coordination_complex) and [catalysts](/source/Catalysis).[6]

## Codes that support ONIOM

- [Gaussian](/source/Gaussian_(software))
- [NWChem](/source/NWChem)
- [ORCA (quantum chemistry program)](/source/ORCA_(quantum_chemistry_program))

## See also

- [QM/MM](/source/QM/MM)
- [Steric effects](/source/Steric_effects) (ONIOM to separate Steric effects vs. electronic effects)

## External links

- [Morokuma Group Home Page](http://kmweb.fukui.kyoto-u.ac.jp/top/index.html)

## References

1. ["Investigating the Reactivity and Spectra of Large Molecules with ONIOM | Gaussian.com"](https://gaussian.com/oniom_technote/). *gaussian.com*. Retrieved 2023-04-13.

1. S. Dapprich; I. Komaromi; K.S. Byun; K. Morokuma; & M.J. Frisch (1999). "A new ONIOM implementation in Gaussian98. Part I. The calculation of energies, gradients, vibrational frequencies and electric field derivatives". *Journal of Molecular Structure: THEOCHEM*. **461-462**: 1–21. [doi:10.1016/S0166-1280(98)00475-8](https://doi.org/10.1016/S0166-1280(98)00475-8)

1. Vreven, T & Morokuma, K (2006). "Chapter 3 Hybrid Methods: ONIOM(QM:MM) and QM/MM". *Annual Reports in Computational Chemistry*. **2**: 35–51. [doi:10.1016/S1574-1400(06)02003-2](https://doi.org/10.1016/S1574-1400(06)02003-2). ISBN 9780444528223.

1. Svensson, Mats; Humbel, StéPhane; Froese, Robert D. J.; Matsubara, Toshiaki; Sieber, Stefan; Morokuma, Keiji (1996). "ONIOM: A Multilayered Integrated MO + MM Method for Geometry Optimizations and Single Point Energy Predictions. A Test for Diels−Alder Reactions and Pt(P(t-Bu)3)2+ H2Oxidative Addition". *The Journal of Physical Chemistry*. **100** (50): 19357. [doi:10.1021/jp962071j](https://doi.org/10.1021/jp962071j)

1. Senn, H & Thiel, W (2007). "QM/MM studies of enzymes". *Current Opinion in Chemical Biology*. **11** (2): 182–7. [doi:10.1016/j.cbpa.2007.01.684](https://doi.org/10.1016/j.cbpa.2007.01.684). [PMID 17307018](https://pubmed.ncbi.nlm.nih.gov/17307018)

1. Ananikov, Valentine P.; Musaev, Djamaladdin G.; Morokuma, Keiji (2010). "Real size of ligands, reactants and catalysts: Studies of structure, reactivity and selectivity by ONIOM and other hybrid computational approaches☆". *Journal of Molecular Catalysis A: Chemical*. **324** (1–2): 104–119. [doi:10.1016/j.molcata.2010.03.015](https://doi.org/10.1016/j.molcata.2010.03.015)

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Adapted from the Wikipedia article [ONIOM](https://en.wikipedia.org/wiki/ONIOM) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/ONIOM?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.