I was looking at how to use LAMMPS to calculate potential energy surface . And I have found that there is a way to calculate PES using fix restrain method (http://lammps.sandia.gov/doc/fix_restrain.html).
I was testing this method to compute PES of ethane (dihedral H-C-C-H). But the result does not look right. I mean the maxima should be at 0, 120 … dgree and minima should be at 60, 180 …degree. However my result shows maxima at 60, 180 and minima at 0, 120.
FYI, I used GAFF, low temperature 0 high temperature 600 restraint coeffs 0 and 3000, angle for 0 to 360.