Local-moment collapse in compressed samarium metal

We present theoretical evidence that the recently observed ultra-high-pressure phase in samarium metal is a delocalized 4f-electron system with an itinerant spin moment of ∼4${\mathrm{\mu }}_{\mathit{B}}$. By comparing the total energy (at T=0) of the localized fcc phase and the delocalized bct phase we conclude that Sm metal will undergo a delocalization of the 4f shell in the Mbar pressure range. This is consistent with the previous experimental observation of an fcc→bct transition at ∼1 Mbar. Furthermore, our calculations show that the correct crystal structure (bct) is obtained only for delocalized 4f states, and the calculated c/a ratio (1.70) compares well with experimental data (1.76).