The Born–Mayer equation is an equation that is used to calculate the lattice energy of a crystalline ionic compound. It is a refinement of the Born–Landé equation by using an improved repulsion term.
E = − N A M z + z − e 2 4 π ϵ 0 r 0 ( 1 − ρ r 0 ) where:
NA = Avogadro constant;M = Madelung constant, relating to the geometry of the crystal;z+ = charge number of cationz− = charge number of anione = elementary charge, 1.6022×10−19 Cε0 = permittivity of free space4πε0 = 1.112×10−10 C2/(J·m)r0 = distance to closest ionp = a constant dependant on the compressibility of the crystal; 30 pm works well for all alkali metal halides