I have another doubt. I am trying to calculate the aqueous stability of GaP at pH 9 and potential 1.5 vs RHE as given in the paper by Singh et. al. (Chem. mater. 2017, 29, 10159-10167)
From the pourbaix entry I got the entry as
Multiple Pourbaix Entry : with energy = -3.7451, npH = -10.0, nPhi = -8.0, nH2O = 5.5, entry_id = [‘mp-886’, ‘ion-13’], species: Ga2O3(s) + PHO4[2-]
The energy per atom for GaP, I got -0.406 eV/atom (MP database)
So following the given eqn, G = G0 + 0.0591 log10(conc) - nO mu_H2O + 0.059*(nH - 2nO) pH + phi (-nH + 2nO + q)
at conditions pH 9 and pot. 1.5 and conc 10e-6. The formation energy for water is -2.46 eV. I guess G0 would be -3.7451, q = -2 and using phi = -1.5
Then Decomposition energy should be
(-7.8791)(from eq) - (-0.81)(from GaP) = -7.0791 eV
So delGpbx per atom would be 3.53 eV/atom. But the given value is 8.15 in the paper.
I am not able to understand, what I am missing or where is the wrong I am doing.
Thank you very much.