The interaction of an ion with all ions in KCL crystal structure deducing its relationship as $?_? = −|?| ? ^2 /? + ? ?_? / ?^?$

please, if someone can answer this question?
deduce the relationship of the interaction of an ion with all ions in KCL crystal structure as $?_? = −|?| frac{?^2}{?} + ? frac{?_?}{?^?}$