# Simulating tripeptide with D-Amino Acids

**URL:** <https://gromacs.bioexcel.eu/t/simulating-tripeptide-with-d-amino-acids/11973>\
**Category:** User discussions\
**Tags:** forcefield\
**Created:** [April 23, 2025, 8:24am UTC](https://gromacs.bioexcel.eu/t/simulating-tripeptide-with-d-amino-acids/11973 "2025-04-23T08:24:26Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![aydatazh](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/aydatazh/32/3346_2.png) [@aydatazh](https://gromacs.bioexcel.eu/u/aydatazh)\
**Post date:** [April 23, 2025, 8:24am UTC](https://gromacs.bioexcel.eu/t/simulating-tripeptide-with-d-amino-acids/11973/1 "2025-04-23T08:24:26Z")

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GROMACS version:2024.1  
GROMACS modification: No  
Force Field used: amber99sb.ff  
I’m trying to modify the amber99sb.ff Foce Field for simulating the tripeptide containing D amino acids.  
I adjusted parameter in this force field and wrote CDT instead of CT and change the aminoacid’s name; DALA instead of ALA.  
Now I want to know how to edit my pdb file.  
I guess change the Cα atoms type and change the resname for example DAL because this column can have three letters in pdb file.  
Subseguently I need to re-editing the force field.  
Do you think these steps are correct and functional?