# Is There an Acceptable Potential Which Can Represent the Interaction between Finite-sized Ions?

The question is as mentioned in the title. Take for example the interaction between $\ce{Ar^+}$ and $\ce{Ar^+}$. In general, is there an acceptable potential which can represent the interaction between $\ce{X^{m+}}$ and $\ce{X^{n+}}$, where $\ce{X}$ is a given element and $m,n=0, \cdots, Z$, where $Z$ is the atomic number of the element $\ce{X}$?

In many cases the coulomb potential (e.g. $V(r) = 1/r$) suffices. However, when density increases (e.g. at liquid/solid density), the size of the positive ion might become relevant.

• The Lennard-Jones and Morse potentials are both "acceptable," depending on just what you're simulating - are you focusing on liquid and solid phases? – Todd Minehardt Jul 26 '15 at 14:55
• Thanks for your reply. Lennard-Jones is fine for inter-atomic interactions. Morse seems to be used for particles bound in a molecule. Indeed I'm interested in a plasma model in which charged species, $X^{+}, \cdots, X^{Z+}$, may exist. In the absence of screening (by free electrons), the potential should have a Coulomb tail (i.e. $\sim m/r$, for some $m$). What I'm looking for is something like the Coulomb-Buckingham potential (en.wikipedia.org/wiki/Buckingham_potential). – Jamie Jul 27 '15 at 3:05
• I'd also like to note that for highly charged species, the coulomb interaction should dominate in short ranges. On the other hand, I'm not so sure about whether there is a distance (which is comparable to the "size" of the ion) at which the repulsion due to the "size" of the ion will dominate over the coulomb repulsion. – Jamie Jul 27 '15 at 3:12