We computed two dimensional PES by running constrained geometry optimizations at a grid of points along two predefined scan coordinates. Based on prior analyses of these motors and our own trial results, we chose two combinations of scan coordinates: central torsion angle 18-15-14-10 combined with pyramidalization 14-1-13-15, and central torsion angle 18-15-14-10 combined with rotor pucker 27-15-16-25.