Ionic Bonds and ionic Crystals

[didy]

is that at equilibrium, energy,U=0 from the equation below?
U(R) = −(A /R6 )+ (B/R12 )
i nid to differentiate the equation and equate U=0?

[alxm]

Read the forum rules. You're not going to get help without having shown you've made some effort to solve what's obviously a homework problem.

Really. If you think ionic forces are involved here, you need to open your textbook.