The Kapustinskii equation calculates the lattice energy U for an ionic crystal, which is experimentally difficult to determine. It is named after Anatoli Fedorovich Kapustinskii who published the formula in 1956.
The calculated lattice energy gives a good estimation for the Born–Landé equation; the real value differs in most cases by less than 5%.  
Furthermore, one is able to determine the ionic radii (or more properly, the thermochemical radius) using the Kapustinskii equation when the lattice energy is known. This is useful for rather complex ions like sulfate (SO) or phosphate (PO).