[lammps-users] asymmetric dihedral angle potential


I need to define a dihedral angle potential which is not symmetric about 0 degree,
Something like the dihedral_style charmm and class2 but maybe more parameters.
For example, in dihedral_style charmm, a non-zero phase shifting parameter d can
make the potential is not symmetric about zero. But there are only one cosine term
in that function which is insufficient for the potential I want. But I think I could
manage to compose a complex function by using more terms.

Now what I would like to know is
1. How the torsional angle is defined in lammps.? [0,pi] or [-pi, pi] or [0,2pi]?
2. Under what circumstance, one should/could use phase shift parameter?
    In CFF91, I see it is always 0. I don't know how it is used in Charmm.
3. Is there possibility to use tabulated potential for dihedrals? (Most probably is not)


Most of your questions are asking for things LAMMPS doesn't
do - you'd have to write these new dihedral potentials yourself,
using a current LAMMPS one as a starting point.

I'd look in the code to see about 0,2*pi vs -pi,pi - it probably doesn't
matter, but you could make sure that way.

No one has written a dihedral_style table, but it could be
done, so long as you had just one free param (the torsion