Abstract
Explicit expressions are derived for the macroscopic and the internal strain in the crystals of the diamond structure with (001) surfaces subject to a stress applied from the sides parallel to the (001) direction. The numerical predictions of the surface relaxation at the ideal (001) surfaces of C, Si, Ge and alpha -Sn crystals are given in terms of the valence force constants already used for the description of the dynamics of the materials. The results are compared with the existing experimental observations.