  Change in the interatomic spacing of a two-atom system under tension and
compression has been modelled by the elastic deformation of atoms. The critical
elastic strain of atoms before separation or cracking from tension was
estimated by the Griffith theory together with a recent mechanics model, then
extended to the lateral elastic expansion under uniaxial compression. The
hypothesis of deformable atoms has led to astonishing predictions of the
critical elastic strain, around 10 and 20 percent for silicon in the 110 and
100 crystal directions. Superimposed by the substantial reduction of
interatomic spacing in the direction of uniaxial compression above 20 GPa,
these severely deformed silicon atoms or metastable new variants have acquired
unforeseeable characteristics and properties, vastly different from those of
silicon atoms under moderate stresses. Under extreme pressure, the natural
repulsive reaction of atoms is intensified due to the increasing alignment of
electron orbitals along the pressure direction and formation of metastable
pressure-resistant phases. An opportunity for creation of a superconductive
band has thus arisen at the edge of the laterally elastically expanded region
away from the nuclei, where more space is available for free electron movement.
Diamond results were also used to validate the new mechanics model, including
the effects of atomic scale defects on fracture strain and strength, critical
to elastic strain engineering.
