Motivated by the newly discovered Co-based superconductor ${\mathrm{Na}}_2{\mathrm{CoSe}}_2\mathrm{O}$, we performed systematic calculations of its electronic band structures using the density functional theory plus the dynamical mean-field theory approaches. Our comparative studies reveal the weakly correlated and itinerant nature of the Co $3d$ electrons and show no sign of fluctuating local moments as expected in many other unconventional superconductors, although the Co $e_g$ orbitals are close to half filling. These suggest that ${\mathrm{Na}}_2{\mathrm{CoSe}}_2\mathrm{O}$ is a normal paramagnetic metal and its superconductivity might not be of strongly correlated nature, contrary to the initial speculation. We suggest future investigations of electron-phonon interactions to clarify its pairing mechanism.

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• Density of states
• Electronic structure
• DFT+DMFT
• DFT+U
• Electron-correlation calculations