[gmx-users] multiple dihedral definition and free energy calculation

francesco oteri francesco.oteri at gmail.com
Tue May 22 18:37:49 CEST 2012

Dear gromacs users,
I am trying to run free energy calculation using the CHARMM force-field.
I am able to generate the .top file, but when I try to obtain the .tpr,
grompp gives the following error:

ERROR 1 [file rest2.top, line 11420]:
  Cannot automatically perturb a torsion with multiple terms to different
  Please specify perturbed parameters manually for this torsion in your

So, I am trying to solve the problem converting the multiple dihedral
definitions in the unique and
equivalent Ryckaert-Bellemans.

Is it in your opinion a correct idea?
Is there any reference I can find where the conversion is easly explained?

Thank you,

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