The Born–Landé equation is a means of calculating the lattice energy of a crystalline ionic compound. In 1918 Max Born and Alfred Landé proposed that the lattice energy could be derived from the electrostatic potential of the ionic lattice and a repulsive potential energy term.
where:
*N =  Avogadro constant;
*M = Madelung constant, relating to the geometry of the crystal;
*z = numeric charge number of cation
*z = numeric charge number of anion
*e = elementary charge, 1.6022 C
*&epsilon; = permittivity of free space
*:4π&epsilon; = 1.112 C/(J·m)
*r = distance between closest cation [ +ve ] & anion [ -ve ].
*n = Born exponent, typically a number between 5 and 12, determined experimentally by measuring the compressibility of the solid, or derived theoretically.
*E = Lattice energy is expressed by E .