first order derivative is 0. when r is close to, recall that the n (usually 1 to 6) is smaller than m (usually 9 to 12), ignore the second term, evaluate the second derivative Recall the relationship between r and Ω In many cases, such as in metal or ionic material, the attraction force is electrostatic, so n = 1, we have This applies to atoms with similar bonding nature. This relationship is verified within alkali metals and many ionic compounds. See also Elasticity tensor References Further reading Elasticity (physics) Physical quantities