QUADRATIC FORCE-CONSTANT OF A CLEAVED JELLIUM AND ITS RELATION TO QUADRATIC RESPONSE FUNCTIONS OF THE HOMOGENEOUS JELLIUM

Rigorous expressions are derived yielding the quadratic force constant B of a jellium interface in terms of the quadratic density-potential response function and the quadratic dielectric function, respectively, of the homogeneous jellium. For the quadratic dielectric function an exact formula including quadratic exchange and correlation corrections is obtained. B is calculated analytically within the local density approximation and numerically within the gradient expansion method using different values of the bulk density. The connection of the linear and quadratic force constants with the jellium cleavage fracture strength and the fracture strength separation is discussed.