# Pdb2gmx with disulfide bond

**URL:** <https://gromacs.bioexcel.eu/t/pdb2gmx-with-disulfide-bond/380>\
**Category:** User discussions\
**Created:** [June 26, 2020, 6:22pm UTC](https://gromacs.bioexcel.eu/t/pdb2gmx-with-disulfide-bond/380 "2020-06-26T18:22:56Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![tns45](https://avatars.discourse-cdn.com/v4/letter/t/dec6dc/32.png) [@tns45](https://gromacs.bioexcel.eu/u/tns45)\
**Post date:** [June 26, 2020, 6:22pm UTC](https://gromacs.bioexcel.eu/t/pdb2gmx-with-disulfide-bond/380/1 "2020-06-26T18:22:57Z")

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GROMACS version: 2018  
GROMACS modification: No

I’m a new GROMACS user and I am trying to convert a pdb file containing two molecules connected by a disulfide bond. The documentation says to use -chainsep or -merge but I still do not understand how exactly in terms of syntax and such am I supposed to use them. Any suggestions? Thank you