Hello,
I saw this question by a user and tried to reproduce the calculation of the formation energy for CoO₂ (mp-1400906) myself.
The data I used, fetched using the API:
=== CoO₂ Results ===
Task ID: mp-2049438
Final Energy: -113.542808 eV
Number of Atoms: 12
Energy per Atom: -9.461901 eV/atom
=== Co Results ===
Task ID: mp-1945908
Final Energy: -13.234231 eV
Number of Atoms: 1
Energy per Atom: -13.234231 eV/atom
=== O₂ Results ===
Task ID: mp-1933400
Final Energy: -39.583688 eV
Number of Atoms: 8
Energy per Atom: -4.947961 eV/atom
This gives a calculated formation energy:
E_f = -9.461901 + \frac{13.234231}{3} + \frac{2 \times 4.947961}{3}
= 1.761549\ \text{eV/atom}
which is different from the reported value of −1.072 eV/atom.