Method of obtaining the stable unit-cell shape in the strained superlattice

A method is presented for the determination of the deformation of the unit cell of a crystal consisting of atoms bound by a three-body potential energy such as that in the Keating model. This method is based on the idea that the potential energy depends on the unit-cell shape only through the metric tensor of the primitive lattice vectors. The method is applied to obtain the stable structure of strained layer superlattices (GaP${)}_{1}$(InP${)}_{1}$(111) grown on GaAs(001) substrates. The c axis perpendicular to the substrate surface is predicted to be inclined 0.7\ifmmode^\circ\else\textdegree\fi{}.