Question

In Lennard-Jones potential, what ε, σ and r represent?

Answer 1

epsilon is the "strength of the potential". Its value is the absolute value of the potential when two particles are at equilibrium with respect to each other. sigma is the "zero crossing" of the potential. Its the distance where the energy between two particles changes from positive to negative. And r is the distance between the two particles under question.

Answer 2

The two particles referred to above are neutral atoms or molecules see http://en.wikipedia.org/wiki/Lennard-Jones_potential

Answer 3

Either. When using the Lennard-Jones potential, we typically approximate the particles as hard spheres. That is, we neglect any internal structure.

Answer 4

thanks a lot :)

Answer 5

which one of \[(\frac{ σ }{ r })^{12}\] and \[(\frac{ σ }{ r })^{6}\] is represents attractive and which one represents repulsive forces?

Answer 6

Assuming you're looking at the standard 12-6 Lennard Jones potential:\[V = 4\epsilon \{ (\frac{\sigma}{r})^{12} - (\frac{\sigma}{r})^{6} \}\]Then the ^12 is repulsive and the is ^6 the attractive part. But don't think about the term itself as being attractive or repulsive, the real culprit is the sign of the term. Negative potential = attraction, positive potential = repulsion.