One of the challenges of thermodynamic modelling has been in accurately representing the vacancies in ordered compounds, which can have a wide range of stability. Individual defect energies of formation are difficult to measure experimentally, and such data is not included explicitly in phase diagram assessments. In recent years, it has become possible to use Density Functional Theory (DFT) to calculate the formation energy of vacancies, or other point defects, with accuracy comparable to experiment . In many systems, no reliable experimental data is available. We show here how such DFT data  can be used to inform the assessment of a phase diagram, with reference to the carbon-zirconium system.
 Nazarov, R.; Hickel, T.; Neugebauer, J., Vacancy formation energies in fcc metals: Influence of exchange correlation functionals and correction schemes. Physical Review B 2012, 85 (14), 144118-1-7.
 Duff, A.I. et al. to be published