# I would like to create a special index group consisting of protein and lipids (POPG/POPE)

**URL:** <https://gromacs.bioexcel.eu/t/i-would-like-to-create-a-special-index-group-consisting-of-protein-and-lipids-popg-pope/2644>\
**Category:** User discussions\
**Tags:** grompp\
**Created:** [August 5, 2021, 12:19pm UTC](https://gromacs.bioexcel.eu/t/i-would-like-to-create-a-special-index-group-consisting-of-protein-and-lipids-popg-pope/2644 "2021-08-05T12:19:02Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![AmitC21](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AmitC21](https://gromacs.bioexcel.eu/u/AmitC21)\
**Post date:** [August 5, 2021, 12:19pm UTC](https://gromacs.bioexcel.eu/t/i-would-like-to-create-a-special-index-group-consisting-of-protein-and-lipids-popg-pope/2644/1 "2021-08-05T12:19:02Z")

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GROMACS version: 2021.2  
GROMACS modification: Yes/No  
Here post your question

Please help me to section and merge of group, i am new user and little confused which number i have to choose?  
Our Bi-layer model comprises of POPG/POPE. (Generted from Membrane builed)

Version- gmx make\_ndx, 2021.2  
Command used- gmx make\_ndx -f em.gro -o index.ndx

- 0 System : 42590 atoms
- 1 Protein : 544 atoms
- 2 Protein-H : 250 atoms
- 3 C-alpha : 34 atoms
- 4 Backbone : 102 atoms
- 5 MainChain : 134 atoms
- 6 MainChain+Cb : 164 atoms
- 7 MainChain+H : 166 atoms
- 8 SideChain : 378 atoms
- 9 SideChain-H : 116 atoms
- 10 Prot-Masses : 544 atoms
- 11 non-Protein : 42046 atoms
- 12 Other : 42046 atoms
- 13 DOPG : 3668 atoms
- 14 POPE : 17500 atoms
- 15 POT : 41 atoms
- 16 CLA : 17 atoms
- 17 TIP3 : 20820 atoms

I was selected 1|13 and index was genrated. When I ran this command (gmx grompp -f NVT.mdp -c em.gro -p topol.top -n index.ndx -o nvt.tpr ) I got this error.

ERROR 1…

ERROR 125 [file PROA.itp, line 2687]:  
No default Position Rest. types

ERROR 126 [file DOPG.itp, line 1229]:  
Incorrect number of parameters - found 2, expected 3 or 6 for Position  
Rest. (after the function type).

There were 2 notes

* * *

Program: gmx grompp, version 2021.2  
Source file: src/gromacs/gmxpreprocess/toppush.cpp (line 2104)

Fatal error:  
There were 126 errors in input file(s)

Please help me to fix this problem. Thank you!

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**Author:** ![mr\_dizzy](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@mr\_dizzy](https://gromacs.bioexcel.eu/u/mr_dizzy)\
**Post date:** [August 5, 2021, 1:44pm UTC](https://gromacs.bioexcel.eu/t/i-would-like-to-create-a-special-index-group-consisting-of-protein-and-lipids-popg-pope/2644/2 "2021-08-05T13:44:10Z")

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Hi,  
the way you generate index file and define merged groups Protein and DOPG is correct. If you want to add also POPE then it should be: 1|13|14.  
But if you read carefully errors, the problem is in PROA.itp or DOPG.itp files where some parameters are missing. Check them.

See ya.

```
Ondrej
```