Ab initio study of the mechanical stability criteria in BeSe and BeTe under hydrostatic pressure

The mechanical stability of homogeneous crystals has been the subject of ex tensive theoretical and computational studies. It has been suggested that B orn stability conditions are only valid for the analysis of an unstressed l attice. The generalization of the elastic stability criteria to the non-zer o stress case can be done by formulating the stability criteria in terms of the elastic stiffness coefficients instead of the elastic constants. In th is paper we present results of the study of stability criteria of Be chalco genides, BeSe and BeTe, from first principles calculations, under hydrostat ic pressure. Our results show the validity of the generalized criteria, in reasonable good agreement with previous experimental and theoretical result s, and suggest the connection between the mechanical instability and the st ructural transition.