  GW approximation is one of the most popular parameter-free many-body methods
that goes beyond the limitations of the standard density functional theory
(DFT) to determine the excitation spectra for moderately correlated materials
and in particular the semiconductors. It is also the first step in developing
the diagrammatic Monte Carlo method into an electronic structure tool, which
would offer a numerically exact solution to the solid-state problem. Currently,
most electronic structure packages support GW calculations for the
band-insulating materials, while the support for the metallic system remains
limited to only a few implementations. The metallic systems are challenging for
GW, as it requires one to accurately resolve the Fermi surface singularities,
which demands a dense momentum mesh. Here we implement GW algorithm within the
all-electron Linear Augmented Plane Wave framework, where we pay special
attention to the metallic systems, the convergence with respect to momentum
mesh and proper treatment of the deep laying core states, as needed for the
future variational diagrammatic Monte Carlo implementation. Our improved
algorithm for resolving Fermi surface singularities allows us a stable and
accurate analytic continuation of imaginary axis data, which is carried out for
GW excitation spectra throughout the Brillouin zone in both the metallic and
insulating materials, and is compared to numerically more stable contour
deformation integration technique. We compute band structures for elemental
metallic systems Li, Na, and Mg as well as for various narrow and wide bandgap
insulators such as Si, BN, SiC, MgO, LiF, ZnS, and CdS and compare our results
with previous GW calculations and available experiments data. Our results are
in good agreement with the available literature.
