Syntax:DihedralAngle(Point1, Point2, Point3, Point4 [, RadDeg] )
Description: Returns the dihedral angle of the angle defined by the four points.
The dihedral angle is the angle between two planes. The first plane is defined by
points 1, 2 and 3. The second plane is defined by points 2, 3 and
PointN: XYZ coordinates of atom N.RadDeg:
Return the angle in radians (=0) or degrees (= 1)