[gmx-users] Incorrect number of parameters in improper dihedral

[Abhishek Acharya]

Hello,

In the OPLSAA ffbonded.itp, it is also mentioned that improper torsions for
planar groups are implemented in gromacs as proper dihedrals. So, I think
you are using the wrong function type here (type 2); you should use type 1
in this case.

Hope this helps.

Best,
Abhishek


On Tue, Jul 17, 2018 at 6:05 AM, Debadutta Prusty <
debaduttaprusty1.2015 at u.northwestern.edu> wrote:

> Hi everyone,
>
> I ran an energy minimization run on a single polymer chain. On running the
> gmx grompp  -f  .mdp ...., I get the following error message:
> "ERROR 1 [file topol.top, line 1486]:
>  Incorrect number of parameters - found 3, expected 2 or 4 for Improper
>  Dih."
>
> The corresponding line(line 1486) in the topology file is:
> ;  ai    aj    ak    al funct            c0            c1
> c2            c3
>     8     7     1    15     2    improper_X_CA_Y_Z
>
> The entry containing the definition of this forcefield in the ffbonded.itp
> (I am using opls all atom force field) file is
> ; X-CA-Y-Z improper torsion. CA is any ring carbon in pyridine
> #define improper_X_CA_Y_Z       180.0     10.460     2
>
> The topology file for the above polymer was generated by using the command
> pdb2gmx(it operated on the pdb file of the polymer chain).
>
> Please help me out.
> --
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