Calculation of surface stress in a linear combination of atomic orbitals representation

A method is presented for separating ``bulk'' and ``surface'' contributions to the strain derivative of the total energy of a two-dimensionally periodic, several-layer slab. The method, involving a layerwise decomposition of the sums and integrals required to calculate the derivative, makes it possible to compute a surface stress via a single, linear combination of atomic orbitals slab calculation. Application to Al(111) yields a predicted tensile surface stress of magnitude 0.090 eV/A².