[gmx-users] opls dihedral function

[Frauke Meyer]

Hi,

I am trying to figure out how the parameters for OPLS dihedrals 
are set and are confused about the different protein/polymer
conventions.

Parameters V_1 and V_3 of the opls dihedral potential are zero
for dihedrals of flat groups like in aromatic rings.
For these cases V_0 is positive and V_2 = -V_0

Thus the function is simply
V = V_0 - V_0 (1 - cos(2phi))   (see eq 4.59 in the manual)
  = V_0 cos(2phi)
But this gives maxima for phi=0 and phi=180 (V=V_0) and mimima
for phi=90 and phi=270 (V=-V0). Shouldn't it be vice versa?

Confused
Frauke