  Recent developments in higher-order topological phases have elucidated on the
relationship between nontrivial multipole moments in the bulk and the emergence
of fractionally quantized charges at the boundary. Here, we put on the table a
proposal of the three-dimensional octupole insulator with fractionally
quantized corner charges $\pm e/8$: sodium chloride, commonly known as table
salt. The fractional quantization of the corner charge is unaffected by the
quantum fluctuation of the electric charge per ion, as we demonstrate
explicitly with ab initio calculations. We further show that the electrostatic
signature of the fractional charge is well-preserved even when the ideal
crystal is sprinkled with defects, and provide a systematic analysis on how the
corner charge contribution could be isolated from the electric-field
corrections originating from realistic surface relaxation. Our results suggest
that the observation of corner charges from quantized multipole moments in
solids might be around the corner.
