ON THE RELATIVE ENERGIES OF SIMPLE METALLIC STRUCTURES

The asymptotic form of the two-body interatomic potentials arising from pseudopotential theory, V(r) = V 0 cos ( 2k F r) (2k F r ) 3 , is used to discuss the relative cohesive energies of simple metallic structures. Use of this potential allows the thermodynamically preferred structure of a simple metallic element or solid solution at 0K to be determined as a function of valence only. The appropriate lattice sums are performed exactly for the f.c.c., h.c.p. (with ideal axial ratio) and b.c.c. structures. In addition, the approximate interplanar interaction of Blandin et al. is summed for polytypic structures. Two modifications of the potential are also considered. First, a phase shift of 2δ is used to obtain a potential of the form, V(r) = V 0 cos ( 2k F r) (2k F r ) 3 . Secondly, the interplanar interaction is adjusted to reflect conditions that might hold when polytypic structures other than f.c.c. and h.c.p. occur. Results for the relative energies of the structures are presented. These results are compared with the observed structures of metallic elements and random solid solutions.