  A combination of the density functional theory and the single-site dynamical
mean-field theory is employed to study the electronic structures of various
allotropes of elemental curium (Cm-I, Cm-II, and Cm-III). We find that the 5$f$
valence electrons in the high-symmetry Cm-I and Cm-II phases remain localized,
while they turn into itinerancy in the low-symmetry monoclinic Cm-III phase. In
addition, conspicuous quasiparticle multiplets are identified in the 5$f$
electronic density of states of the Cm-III phase. We believe that it is the
many-body transition between $5f^{7}$ and $5f^{8}$ configurations that gives
rise to these quasiparticle multiplets. Therefore, the Cm-III phase is probably
a new realization of the so-called Racah metal.
