  Freezing of simple liquid metals and the relative stabilities of competing
crystalline solids are investigated using thermodynamic perturbation theory,
the interactions between ions being modeled by effective pair potentials
derived from pseudopotential theory. The ionic free energy of the solid phase
is calculated, to first order in the perturbation potential, using classical
density-functional theory and an accurate approximation to the hard-sphere
radial distribution function. Free energy calculations for Na, Mg, and Al yield
well-defined freezing transitions and structural free energy differences for
bcc, fcc, and hcp crystals in qualitative agreement with experiment.
