is the standard Gibbs free energy calculated from H • 350K and S • 350K , the standard enthalpy and entropy respectively, both taken from the NIST-JANAF thermodynamics tables. P is the pressure, P • is the reference pressure and E DFT is the total DFT energy of an oxygen molecule. Throughout the study, we use the pressure as a reference, since it is the only variable term in Equation . We study a broad range of pressures from 10 -25 to 1.0 atm at the same temperature of 350 K.