Hi, energies of materials on MP are typically reported to the fourth decimal place. For example NaCl: -3.3881 eV. (found here: https://materialsproject.org/materials/mp-22862/#calculation-summary)

Does this mean a numerical precision of -3.3881 ± 0.0001 eV/atom ?

My doubts come from the Materials Project Documentation (https://docs.materialsproject.org/methodology/total-energies/):

In the “Total energy convergence” chapter it says that “96% of compounds tested were converged to within 15 meV / atom.”

Does this mean that I have to assume for every energy reported on MP a worst-case numerical precision of 15 meV?

In the case of NaCl this would give -3.38 ± 0.015 eV/atom ?

Hello Victor,

Well, the numerical precision might be up to 4 digits (i.e., the precision you get if you reran the exact same calculation twice), however, what matters is the **convergence** accuracy of DFT (i.e., to what extent is the energy value converged w.r.t. the plane wave energy cutoff, number of k-points, etc.). And as you already mentioned, this is explained in the link you shared:

Using a 500 pra k-point mesh, the numerical convergence for most compounds tested was within 5 meV/atom, and 96% of compounds tested were converged to within 15 meV/atom. Results for the new parameter set will be better due to the denser k-point mesh employed. Convergence will depend on chemical system; for example, oxides were generally converged to less than 1 meV/atom.

-Peter