$5\mathrm{.}2$ Taking into account both attractive and repulsive interactions, derive an equation

analogous to Equation $(5\mathrm{.}2)$ for the $CsCl$ structure $($Figure $1\mathrm{.}40).$ Include the first four

terms in the Madelung series. Hint: You may find this easier to do in terms of the cell

edge $a,$ and then convert to the interatomic distance $d$ that is normally used in Madelung

formulas,