# Is it possible to apply multiple force fields?

**URL:** <https://gromacs.bioexcel.eu/t/is-it-possible-to-apply-multiple-force-fields/3566>\
**Category:** User discussions\
**Tags:** forcefield, mdp-parameters\
**Created:** [January 28, 2022, 3:46pm UTC](https://gromacs.bioexcel.eu/t/is-it-possible-to-apply-multiple-force-fields/3566 "2022-01-28T15:46:12Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Tan](https://avatars.discourse-cdn.com/v4/letter/t/f07891/32.png) [@Tan](https://gromacs.bioexcel.eu/u/Tan)\
**Post date:** [January 28, 2022, 3:46pm UTC](https://gromacs.bioexcel.eu/t/is-it-possible-to-apply-multiple-force-fields/3566/1 "2022-01-28T15:46:12Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question Is it possible to apply multiple force fields on a single run? I am looking to simulate a mAb that is glycosylated and came across this paper, where two force fields have been used. [https://pubs.acs.org/doi/pdf/10.1021/acs.jpcb.1c04279](https://pubs.acs.org/doi/pdf/10.1021/acs.jpcb.1c04279) Also, which force field is best for glycosylated mAbs?

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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:** [January 28, 2022, 6:44pm UTC](https://gromacs.bioexcel.eu/t/is-it-possible-to-apply-multiple-force-fields/3566/2 "2022-01-28T18:44:36Z")

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> [@Tan](#):
>
> I am looking to simulate a mAb that is glycosylated and came across this paper, where two force fields have been used. [https://pubs.acs.org/doi/pdf/10.1021/acs.jpcb.1c04279](https://pubs.acs.org/doi/pdf/10.1021/acs.jpcb.1c04279)

GLYCAM is an AMBER-compatible force field. It is a distinct entity but is designed to be used with AMBER, so it’s not two force fields in practice. You can never mix different force fields, but that’s not what is happening here.

> [@Tan](#):
>
> Also, which force field is best for glycosylated mAbs?

AMBER and CHARMM both handle these cases easily, though using GLYCAM requires some force field editing to make the 1-4 scaling factors work. CHARMM does not require any modification. CHARMM-GUI can build these systems easily; they are quite difficult in GROMACS due to the limitations of `pdb2gmx`.

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**Author:** ![Tan](https://avatars.discourse-cdn.com/v4/letter/t/f07891/32.png) [@Tan](https://gromacs.bioexcel.eu/u/Tan)\
**Post date:** [February 2, 2022, 5:55pm UTC](https://gromacs.bioexcel.eu/t/is-it-possible-to-apply-multiple-force-fields/3566/3 "2022-02-02T17:55:52Z")

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Hi Jalemkul,

Thank you for getting back to me.

I am still quite confused on how GLYCAM and AMBER are being leveraged in the paper. Essentially, is GLYCAM an extension of AMBER?

I look forward to hearing from you.

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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:** [February 2, 2022, 6:46pm UTC](https://gromacs.bioexcel.eu/t/is-it-possible-to-apply-multiple-force-fields/3566/4 "2022-02-02T18:46:17Z")

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> [@Tan](#):
>
> Essentially, is GLYCAM an extension of AMBER?

Yes, it is. It was developed to be used in concert with AMBER protein and nucleic acid force fields. While it may have a “different” name, it’s compatible.

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<div class="post-metadata">

**Author:** ![Tan](https://avatars.discourse-cdn.com/v4/letter/t/f07891/32.png) [@Tan](https://gromacs.bioexcel.eu/u/Tan)\
**Post date:** [February 2, 2022, 6:46pm UTC](https://gromacs.bioexcel.eu/t/is-it-possible-to-apply-multiple-force-fields/3566/5 "2022-02-02T18:46:57Z")

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Thank you for clarifying. I really appreciate it!