Many-electron systems are within density functional theory described in terms of an appropriately defined local stress tensor. The differential equation for its exchange and correlation part is solved also for the case of density gradient dependent exchange and correlation energy. Formulae are given (i) for the direct calculation of the global stress tensor of a homogeneously strained crystal via surface integrals of the local stress tensor along intercell boundaries, and (ii) similarly for the energy change of inhomogeneously strained crystals.
 

Zeitschrift fur Physik B, 76 193-8, 1989.