# Problem facing execution of pdb2gmx while using GROMACS 2020

**URL:** <https://gromacs.bioexcel.eu/t/problem-facing-execution-of-pdb2gmx-while-using-gromacs-2020/1031>\
**Category:** User discussions\
**Created:** [November 1, 2020, 5:10pm UTC](https://gromacs.bioexcel.eu/t/problem-facing-execution-of-pdb2gmx-while-using-gromacs-2020/1031 "2020-11-01T17:10:08Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![abhishek](https://avatars.discourse-cdn.com/v4/letter/a/7ba0ec/32.png) [@abhishek](https://gromacs.bioexcel.eu/u/abhishek)\
**Post date:** [November 1, 2020, 5:10pm UTC](https://gromacs.bioexcel.eu/t/problem-facing-execution-of-pdb2gmx-while-using-gromacs-2020/1031/1 "2020-11-01T17:10:08Z")

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GROMACS version: 2020  
GROMACS modification: No  
Here post your question

I am using Gromacs 2020 right now and trying to process my pdb file using the pdb2gmx command. I have kept gromos53a6.ff in my working directory containing all the necessary itp and rtp files. While executing the pdb2gmx command without -ff flag, I’m getting the following message/error.

Feature not implemented:  
Can only select the first of multiple force field entries with directory name  
‘gromos53a6.ff’ in the list. If you want to use the next entry, run pdb2gmx in  
a different directory, set GMXLIB to point to the desired force field first,  
and/or rename or move the force field directory present in the current working  
directory.

While I’m using ff flag and executing the command, I’m getting the following error

Program: gmx pdb2gmx, version 2020  
Source file: src/gromacs/gmxpreprocess/pdb2top.cpp (line 209)  
Function: void choose\_ff\_impl(const char\*, char\*, int, char\*, int)

Inconsistency in user input:  
Could not find force field ‘gromos53a6.ff/’ in current directory, install tree  
or GMXLIB path.

I couldn’t figure out the stuff related to GMXLIB and unable to process my pdb file and create a topology file.

I request you to solve my query.

Kind Regards,

Abhishek

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**Author:** ![cblau](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/cblau/32/5_2.png) [@cblau](https://gromacs.bioexcel.eu/u/cblau)\
**Post date:** [November 2, 2020, 11:04am UTC](https://gromacs.bioexcel.eu/t/problem-facing-execution-of-pdb2gmx-while-using-gromacs-2020/1031/2 "2020-11-02T11:04:39Z")

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Hi Abishek,

using just `gromos53a6` without the `.ff` should help.

Let me know if that solved the issue!