[gmx-users] Linear CG beads, grompp doesn't work

[Xu Dong Huang]

Dear advanced gromac users,

I am trying to simulate a long linear chain of polymer using CG beads. (about 200 beads), all with same type charge interactions. (examples shown:) I read on previous gromacs mailing list that linear systems with same charges make the system unstable? But is there anyway to go around that? 

[atoms]
1	P3	O1	mon	1	0.00
2	P3	O1	mon	2	0.00
3	P3	O1	mon	3	0.00
4	P3	O1	mon	4	0.00
5	P3	O1	mon	5	0.00
6	P3	O1	mon	6	0.00
7	P3	O1	mon	7	0.00
8	P3	O1	mon	8	0.00
9	P3	O1	mon	9	0.00
…….
[ bonds ]
1	2	1	0.43	17000
2	3	1	0.43	17000
3	4	1	0.43	17000
4	5	1	0.43	17000
……

However, when i do grompp -f vac_min.mdp -c mon.gro -p mon.top -o vac.tpr 
-it returns the error of: 
Fatal error:
The largest charge group contains 200 atoms. The maximum is 32.
For more information and tips for troubleshooting, please check the GROMACS
website at http://www.gromacs.org/Documentation/Errors

Please let me know if there is a way to go around that. Thank you. 

Xu Dong Huang
Chemical & Biochemical Engineering
Rutgers School of Engineering 
xudongh at eden.rutgers.edu