ELASTIC-CONSTANTS OF CU AND THE INSTABILITY OF ITS BCC STRUCTURE

First-principles full-potential nonrelativistic calculations of the total energy of fcc Cu for various deformations of the cubic unit cell give values of the three elastic constants of fcc Cu in good agreement with experiment. Use is made of simple formulas for the strain energy of tetragonal and trigonal deformations in terms of the elastic constants. The total energy of Cu as a function of the shape of a body-centered-tetragonal cell at constant volume does not have a minimum at the bcc structure, and it is concluded that bcc Cu is unstable with respect to [110] shears. However, this instability does not prevent epitaxial growth on (001) surfaces.