where r {\displaystyle r} is now the coordinate perpendicular to the surface. This form approaches zero at infinite r {\displaystyle r} and equals − D e {\displaystyle -D_{e}} at its minimum, i.e. r = r e {\displaystyle r=r_{e}} . It clearly shows that the Morse potential is the combination of a short-range repulsion term (the former) and a long-range attractive term (the latter), analogous to the Lennard-Jones potential.