I am trying to plot a ternary phase diagram of Li-Al-O2 system. According to the materials project, the Li9Al4 is unstable in the convex hull of Li-Al binary. When I was calculating the formation energy per atom of different structures, I found that the formation energy of Li9Al4 from my VASP calculation (-0.156 eV) does not match with the reference Li9Al4 (mp-568404) of the materials project (-0.145 eV). I used exactly the same input files as the materials project, however, got different formation energy per atom. Can you please explain the probable reason of such dissimilarities?
Moreover, the attached figure (J. Electrochem. Soc., 2017, 164, 14, A3582-A3589) shows that the Li9Al4 is stable in the convex hull of Li-Al binary.
Thank you very much for your time.