This section shows how to restrain dihedral angles to particular values.
The functional form of the effective
energy 
is given by
where the sum extends over all restrained dihedral
angles and
the square-well potential 
is given by
S is an overall weight factor.
The constant C, the angle range 
,
the angle centroid 
, and the exponent ed are specified
in the restraints dihedral statement. The dihedral
angle can be defined by a set of four atoms independent of
the molecular structure. In particular, the four atoms do not
have to be connected to each other. Each atom is selected
by a separate selection statement. The dihedral angle involving
four atoms i,j,k,l
is defined as the angle between two planes, where the first
plane is made by atoms i,j,k and the other plane
is made by atoms j,k,l.