  The debate whether uranium 5f electrons are closer to being localized or
itinerant in the ferromagnetic compound UGa2 is not yet fully settled. The
experimentally determined magnetic moments are large, approximately 3 Bohr
magnetons, suggesting the localized character of the 5f electrons. In the same
time, one can identify signs of itinerant as well as localized behavior in
various spectroscopic observations. The band theory, employing local
exchange-correlation functionals, is biased toward itinerant 5f states and
severely underestimates the moments. Using material-specific dynamical
mean-field theory (DMFT), we probe how a less approximate description of
electron-electron correlations improves the picture. We present two variants of
the theory: starting either from spin-restricted (LDA) or spin-polarized (LSDA)
band structure. We show that the L(S)DA+DMFT method can accurately describe the
magnetic moments in UGa2 as long as the exchange interaction between the
uranium 6d and 5f electrons is preserved by a judicious choice of the
spin-polarized double-counting correction. We discuss the computed electronic
structure in relation to photoemission experiments and show how the
correlations reduce the Sommerfeld coefficient of the electronic specific heat
by shifting the 5f states slightly away from the Fermi level.

Strongly Correlated Electrons;Materials Science