  The structural, electronic, and magnetic properties of Gd@C_82 endohedral
metallofullerene have been studied by employing on-site correlation corrected,
scalar-relativistic and full-relativistic density functional theory within the
local density and generalized gradient approximations. The experimentally
observed reduction of the magnetic moment of Gd@C_82 with respect to that of a
free Gd^+3 ion can be explained by a tiny hybridization between unoccupied
Gd-4f states and carbon-pi states, resulting in a generic antiferromagnetic
coupling of the Gd-4f spin with the remaining unpaired spin in the hybridized
molecular orbital.
