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

[Debadutta Prusty]

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.