  A DFT-based method is presented which allows the computation of all-electron
NMR shifts of metallic compounds with periodic boundary conditions. NMR shifts
in metals measure two competing physical phenomena. Electrons interact with the
applied magnetic field (i) as magnetic dipoles (or spins), resulting in the
Knight shift, (ii) as moving electric charges, resulting in the chemical (or
orbital) shift. The latter is treated through an extension to metals of the
Gauge Invariant Projector Augment Wave(GIPAW) developed for insulators. The
former is modeled as the hyperfine interaction between the electronic spin
polarization and the nuclear dipoles. NMR shifts are obtained with respect to
the computed shieldings of reference compounds, yielding fully ab-initio
quantities which are directly comparable to experiment. The method is validated
by comparing the magnetic susceptibility of interacting and non-interacting
homogeneous gas with known analytical results, and by comparing the computed
NMR shifts of simple metals with experiment.
