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scGW0 caveats

The scGW0 must be used with great caution, in particular, in combination
with symmetry. Symmetry is handled in a rather sophisticated manner,
specifically, only the minimal number of required combination of and point is
considered. In this case, symmetry must be applied to restore the
full star of . This is done by determining degenerate
eigenvalue/eigenvector pairs and restoring their symmetry according to their
irreducible representation.
Although the procedure is generally rather reliable, it fails to work
properly if the degenerate states do not posses eigenvalues that
are sufficiently close, due to insufficient convergence in
the preceding DFT calculations. States are treated as degenerate
if, and only if, their eigenenergies are within 0.01 eV.

For large supercells with low symmetry, we strongly recommend to
switch off symmetry.

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