How to calculate Formation Energy / Atom on material project?

In mp database, I found the formation energy for water molecules(mp-697111) should be -1.393 eV*3=-4.179/formula.
However, if I search the Final Energy/Atom for H2O(mp-697111), H2(mp-632291) and O2(mp-1091399), each of them is with the smallest e above hull and green highlight. Then I calculated the formation energy for H2O by hands:


Where does the error come from? Similarly, I calculated the formation energy for Mg(OH)2, I found there is also a deviation between the data in MP and data calculated by hands.
This troubles me for a long time if you have any idea, please leave a message, Thanks in advance.


the formation energy is here

Hi @Slame,

The formation energies are in eV/Atom. Dividing your number 3 fixes this discrepancy.

Thanks for your reply!
I know formation energies are in eV/Atom and I calculated the formation energy for the water molecule, -1.393*3 = -4.179 eV/formula.
Mg question is If I search the energy of H2,O2 and H2O in mp database, then I calculate the formation energy by hands(the answer is -3.1765/formula), where this deviation(between -4.179 and -3.1765) come from?

Are you using the corrected energies?

Thank you so much! I fix this problem by using corrected energy