First-principles studies on the pressure dependences of the stress–strain relationship andelastic stability of semiconductors

Abstract

We investigate the stress–strain relationship and elastic stability of zinc-blende GaP, GaN,InP and BN lattices under hydrostatic pressure by first-principles calculation. A simpleand direct ab initio implementation for studying the mechanical properties ofcubic crystals is developed. The four phases’ full-set stress–strain coefficients inwide pressure ranges are theoretically calculated. The fundamental mechanism ofelastic stability and the origin of phase transformation under hydrostatic pressureare explored. We found that the abilities for most of these lattices are enhancedto sustain axial strain but weaken to shear strain under higher pressure. Theconditions of lattice stability are analysed using both the thermodynamic work–energycriterion and the elastic-stiffness criteria. We show that the lattice collapse ofthe perfect crystals is caused by the disappearance of their bulk moduli undervolume dilation. Lattice defects are considered to be the main reason causing phasetransformation under pressure. The correlation between the phonon softening and thevariation of elastic coefficients is studied. The pressure dependence of the Kleinmaninternal strain parameter and its relationship to elastic stability is also explored.