[gmx-users] oplsaa dihedral with minimum at 222 degrees

[Ben Harland]

I am preparing a topology for an opls-aa ATP molecule.  It seems to me that 
one does not yet exist.  I am having difficulties with the dihedral 
parameters:  the OPLS-AA force field uses a RB-type function with a minimum 
at 180 degrees, but our QC data describes a function symmetric about 222 
degrees.  Is there a way to accomodate this offset?  Are there other 
examples of molecules with an equilibrium dihedral angle other than trans?

I have also tried to fit this potential to a number of gromos-type periodic 
functions with no luck.

Thanks in advance,
Ben Harland