Stability region of a close-packed layer of atoms

A rhombic four-atom unit cell corresponding to a close-packed atomic layer is considered, The interatomic forces in the cell are defined by the Morse and Lennard-Jones potentials for large strains. The stability region of the cell is constructed as a function of two parameters that model tension-compression along the major diagonal of the cell and shear. For each point in the stability region, equilibrium states of the cell are determined numerically; at least one of these states is stable. It is shown that for the close-packed atomic layer under combined compression-shear loading, Poisson’s ratio needs to be taken into account.