# Units of Lennard Jones Potential Parameters

**URL:** https://gromacs.bioexcel.eu/t/units-of-lennard-jones-potential-parameters/4595
**Category:** User discussions
**Tags:** forcefield, mdp-parameters, mdrun
**Created:** [August 11, 2022, 10:18pm UTC](https://gromacs.bioexcel.eu/t/units-of-lennard-jones-potential-parameters/4595 "2022-08-11T22:18:20Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![Kal](https://avatars.discourse-cdn.com/v4/letter/k/9de053/32.png) [@Kal](https://gromacs.bioexcel.eu/u/Kal)
#### Post date: [August 11, 2022, 10:18pm UTC](https://gromacs.bioexcel.eu/t/units-of-lennard-jones-potential-parameters/4595/1 "2022-08-11T22:18:20Z")

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GROMACS version:  
GROMACS modification: No  
Here post your question

According to the combination rules, LJ parameters have different units;

 ![01](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/1/1600274616e76b37b59dc2e8a11b3b474997c6ed.png)

How can I convert combination rule 2 or 3 units to combination rule 1 unit?

Cheers, Kal

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### Author: ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)
#### Post date: [August 12, 2022, 2:16am UTC](https://gromacs.bioexcel.eu/t/units-of-lennard-jones-potential-parameters/4595/2 "2022-08-12T02:16:15Z")

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Follow the formulas. For rule 1, C(6) and C(12) are simply computed from σ and ε. It’s not a unit conversion, per se, it’s simply a different way of expression the LJ form.

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### Author: ![Kal](https://avatars.discourse-cdn.com/v4/letter/k/9de053/32.png) [@Kal](https://gromacs.bioexcel.eu/u/Kal)
#### Post date: [September 22, 2022, 4:06am UTC](https://gromacs.bioexcel.eu/t/units-of-lennard-jones-potential-parameters/4595/3 "2022-09-22T04:06:19Z")

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Thank you!