LJ

[classi] [classj] lj [sigma_0] [epsilon_0] [rep] [att]

$$U_{\mathrm{LJ}} = 4 \epsilon_0 \left[ A \left(\frac{\sigma_0}{r}\right)^{12} - B \left(\frac{\sigma_0}{r}\right)^6\right]$$ (4)

Here $A$ is the repulsive coefficient and $B$ is the attractive coefficient. For a typical LJ usage, set $A = B = 1$. For a purely repulsive LJ site, set $A = 1$ and $B = 0$. Some potentials (e.g., TIP4P) use values of $A$ and $B$ that are both not equal to $1$.