[gmx-users] Errors about dihidral angle type 9 in free energy perturbation

[Jianguo Li]

Dear All,
I am trying to use free energy perturbation module of gromacs to do hamiltonian replica exchange using CHARMM27 all-atom force field (with CMAP) - version 2.0

I am using 4.5.4 version of gromacs

according to manual (Table 5.5), it allows to perturb dihedral angles: proper dih. multi,  ftp 9, phi and k are allowed under 'F.E.'

I have edited charmm files( ffbonded.itp and also ffnonbonded.itp) for "state B" parameters.
but when I run simulations, it throws following error (for 23 lines):
"
ERROR 1 [file topol-edited-charmm.top, line 1453]:
  Cannot automatically perturb a torsion with multiple terms to different
  form.
  Please specify perturbed parameters manually for this torsion in your
  topology!
"

What is the fix for this?
Why gromacs is not recognising the 'state B' parameters?

I also tried to do this with higher version of gromacs (including latest). It throws the same error.


Thank you very much for your time. 

Cheers,Jianguo