  We investigate the magnetic phase diagram of the newly discovered iron-based
high temperature oxypnictide superconductors of the type RO$_{1-x}$F$_x $FeAs,
with rare earths R=La, Sm, Nd, Pr and Ce by means of {\it ab initio} SGGA and
SGGA+U density functional computations. We find undoped LaOFeAs to be a Mott
insulator when incorporating electronic correlations via SGGA+U for any
physically relevant value of $U$. The doped compounds are according to SGGA
conductors with a transition from an antiferromagnetic to a non-magnetic state
at a hole doping of concentration $x_c$=0.075 for R=Nd, Pr and at electron
doping $x_c$=0.25 for Ce and 0.6 for Sm. Superconductivity in these rare-earth
oxypnictides thus appears in the vicinity of a magnetic quantum critical point
where electronic correlations are expected to play an important role because of
the vicinity of a Mott insulating state at zero doping.
