dihedral_style for amber

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#1

Dear all,

I am wondering if I can use dihedral_style = charmm in combination with special_bonds = amber.
Reason I am asking is, any time I am changing the dihedral_style from harmonic to charmm I am getting an error.
I checked the data file and there are indeed no dihedral_coeff of the form 1 120.0 1 60 0.5 present; therefore the error.

The Cornell article describes the dihedral potential closer to the charmm dihedral than the harmonic potential.

Thank you very much in advance for your help,
Markus

P.S. The data file has been obtained with AmberTools and converted with the python script provided with Lammps.

#2

LAMMPS doesn't care if you use any dihedral style
with any special_bonds setting. Your problem sounds
like that you do not have the correct dihedral coeffs
listed in the data file for the dihedral style you
are choosing. I am guessing the convertor script
you mention does not write out the correct format for
any dihedral, but only for a particular dihedral style.

If that isn't the style you want, then you would need
to adjust the diherdal coeffs yourself to match the style.

Steve