The Morse Potential
The Morse potential has the form:
The Morse potential may be written as
 
(1) 
where is the pair well depth and r_{0} the equilibrium pair separation.
In reduced units ( and r_{0}=1) there is a single adjustable parameter, ,
which determines the range of the interparticle forces.
The Figure shows that decreasing increases the range of the
attractive part of the potential and softens the repulsive wall, thus widening the
potential well.
The LJ potential
has the same curvature at the bottom of the well as the Morse potential when .
Girifalco has obtained an intermolecular potential for
molecules
which is isotropic and shortranged relative to the equilibrium pair separation,
with an effective value of .
The alkali metals have longerranged interactions, for example
=3.15 has been suggested for sodium.
Fitting to bulk data gives a value of =3.96 for nickel.
Figure:
The Morse potential for different values of the range parameter as indicated.

Reference: P. M. Morse, Phys. Rev.34, 57 (1929).
Jon Doye
11/5/1997