# CO3-- angle modification

**URL:** <https://gromacs.bioexcel.eu/t/co3-angle-modification/10808>\
**Category:** User discussions\
**Created:** [December 13, 2024, 3:05pm UTC](https://gromacs.bioexcel.eu/t/co3-angle-modification/10808 "2024-12-13T15:05:28Z")\
**Posts on this page:** 7\
**Page:** 2

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**Author:** ![GiuseppeP](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@GiuseppeP](https://gromacs.bioexcel.eu/u/GiuseppeP)\
**Post date:** [December 17, 2024, 8:53am UTC](https://gromacs.bioexcel.eu/t/co3-angle-modification/10808/21 "2024-12-17T08:53:59Z")

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Thank you very much! Molecules stay almost all planar.

I have another question. Since the force field I found is used in LAMMPS, do I need to multiply the constant by two, since in LAMMPS potential expression 1/2 does not appear?  
If yes, is it valid for bonds, angles and dihedrals?

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**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [December 17, 2024, 9:10am UTC](https://gromacs.bioexcel.eu/t/co3-angle-modification/10808/22 "2024-12-17T09:10:55Z")

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This is not a quadratic potential, so there is no factor 2 involved.

Unfortunately the paper doesn’t contain formulas for the potentials, but it mentions GROMACS, so I assume the bond and angle potentials have the factor 1/2.

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<div class="post-metadata">

**Author:** ![GiuseppeP](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@GiuseppeP](https://gromacs.bioexcel.eu/u/GiuseppeP)\
**Post date:** [December 17, 2024, 9:24am UTC](https://gromacs.bioexcel.eu/t/co3-angle-modification/10808/23 "2024-12-17T09:24:25Z")

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Summming up, I have to use the constants as they are reported, the dihedral is C O O O at 180° and funct type is 1 with multiplicty 1. Is it right?

Morever, for bond the funct type I used is correct? I’m not sure because of the units of the force constant

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<div class="post-metadata">

**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [December 17, 2024, 9:40am UTC](https://gromacs.bioexcel.eu/t/co3-angle-modification/10808/24 "2024-12-17T09:40:11Z")

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The dihedral is O C O O.

The units for the bond potential in the paper look to be incorrect. I assume it should be kJ/mol/nm^2.

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<div class="post-metadata">

**Author:** ![GiuseppeP](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@GiuseppeP](https://gromacs.bioexcel.eu/u/GiuseppeP)\
**Post date:** [December 17, 2024, 9:44am UTC](https://gromacs.bioexcel.eu/t/co3-angle-modification/10808/25 "2024-12-17T09:44:03Z")

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Using O C O O 180° the molecules are completely deformed

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<div class="post-metadata">

**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [December 17, 2024, 9:51am UTC](https://gromacs.bioexcel.eu/t/co3-angle-modification/10808/26 "2024-12-17T09:51:50Z")

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Then we are back to that the order of the atoms likely is wrong. You would need to swap the order of e.g. the last two hydrogens. Changing 180 to 0 would also fix it.

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<div class="post-metadata">

**Author:** ![GiuseppeP](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@GiuseppeP](https://gromacs.bioexcel.eu/u/GiuseppeP)\
**Post date:** [December 17, 2024, 9:59am UTC](https://gromacs.bioexcel.eu/t/co3-angle-modification/10808/27 "2024-12-17T09:59:28Z")

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I fixed O1 C1 O4 O3 at 180° and it worked. Thank you very much

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