Absence of volume metastability in bcc copper

A previous pseudopotential total-energy calculation on bcc copper revealed a structural metastability in the form of a double-well total-energy curve with two local minima (at 6% compression and 7% dilation relative to the observed equilibrium volume of the fcc structure), separated by a barrier. This was explained in terms of a symmetry breaking in the nonspherical components of the valence-electron charge density upon volume change. Our present all-electron calculation shows no such metastability; analysis of the response of the valence-electron charge density to volume deformations indeed shows no cause for such a metastability.