Error in opls itp file

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1

GROMACS version:2021.4
GROMACS modification: Yes/No
Here post your question : I want to simulate my protein in cyclohexane solvent. The following is my itp file for cyclohexane which was generated using LigPargen-
[ moleculetype ]

8 ; Name nrexcl

9 UNK 3

10 [ atoms ]

11; nr type resnr residue atom cgnr charge mass

12 1 opls_800 1 UNK C00 1 -0.1742 12.0110

13 2 opls_801 1 UNK C01 1 -0.1743 12.0110

14 3 opls_802 1 UNK C02 1 -0.1743 12.0110

15 4 opls_803 1 UNK C03 1 -0.1742 12.0110

16 5 opls_804 1 UNK C04 1 -0.174 12.0110

17 6 opls_805 1 UNK C05 1 -0.1741 12.0110

18 7 opls_806 1 UNK H06 1 0.0871 1.0080

19 8 opls_807 1 UNK H07 1 0.0871 1.0080

20 9 opls_808 1 UNK H08 1 0.0871 1.0080

21 10 opls_809 1 UNK H09 1 0.0871 1.0080

22 11 opls_810 1 UNK H0A 1 0.0872 1.0080

23 12 opls_811 1 UNK H0B 1 0.0872 1.0080

24 13 opls_812 1 UNK H0C 1 0.0872 1.0080

25 14 opls_813 1 UNK H0D 1 0.0872 1.0080

26 15 opls_814 1 UNK H0E 1 0.0871 1.0080

27 16 opls_815 1 UNK H0F 1 0.0871 1.0080

28 17 opls_816 1 UNK H0G 1 0.087 1.0080

29 18 opls_817 1 UNK H0H 1 0.087 1.0080

In the step while adding ions with the -grompp command (gmx grompp -f ions.mdp -c 1AKI_solv.gro -p topol.top -o ions.tpr) , I am getting the following error-

ERROR 1 [file UNK_D2E5F2.itp, line 12]:
Atomtype opls_800 not found

Can anyone please help me solve this?

2

You need to pass a .top that contains atomtype and bonded parameters, your .itp is just an “include topology” file type that builds a complete topology. Some programs will give you .itps to include in your system definitions, but they are not fully functional topology files on their own.

In short, you’ll have to find/include an OPLS forcefield.itp (is included in a standard Gromacs distribution) and follow typical Gromacs topology format specification. Go through any basic Gromacs tutorial to produce a functional topology, and then prepare yours by analogy.