Born–Mayer equation

• N_A = Avogadro constant;
• M = Madelung constant, relating to the geometry of the crystal;
• z⁺ = charge number of cation
• z⁻ = charge number of anion
• e = elementary charge, 1.6022 C
• ε₀ = permittivity of free space
• :4ε₀ = 1.112 C²/
• r₀ = distance to closest ion
• ρ = a constant dependent on the compressibility of the crystal; 30 pm works well for all alkali metal halides