  The tetragonal states produced by isotropic pseudomorphic epitaxial strain in
the (001) plane on a tetragonal phase of a crystal are calculated for V, Ti,
Rb, Li, K, Sr from first-principles electronic theory. It is shown that each
metal has two tetragonal phases corresponding to minima of the total energy
with respect to tetragonal deformations, hence are equilibrium phases, and that
the equilibrium phases are separated by a region of inherent instability. The
equilibrium phase for any strained tetragonal state can thus be uniquely
identified. Lattice constants and relative energies of the two phases and the
saddle point between them are tabulated, as well as the tetragonal elastic
constants of each phase.
