Where is the warning? Probably from the line dividing by energy. If so, it's not so critical, it just means you have a zero energy.
180 and 1000 are wavelengths, computed from the energies on the line commented as "# Calculate the wavelength" and 2.2 and 6.4 and the other ones are needed because axis() take a 4-element list (xmin, xmax, ymin, ymax).