Af. Kohan et G. Ceder, TIGHT-BINDING CALCULATION OF FORMATION ENERGIES IN MULTICOMPONENT OXIDES - APPLICATION TO THE MGO-CAO PHASE-DIAGRAM, Physical review. B, Condensed matter, 54(2), 1996, pp. 805-811
In this work we illustrate how the tight-binding formalism can be used
to accurately compute formation energies in multicomponent oxides. Th
e large and complex unit cells of these systems make the application o
f precise ab initio local-density approximation (LDA) techniques very
computer-time demanding. Consequently, simpler but less accurate metho
ds, such as potential models, are usually used but at the expense of o
btaining just qualitatively correct results. In addition, many ad hoc
assumptions have to be taken in potential models to deal with charge t
ransfer and many-body effects. The tight-binding method can naturally
incorporate these effects in its formalism and still retain a low comp
utational cost. Furthermore, we will show that it can accurately descr
ibe the energetics of oxides once its parameters are fitted to precise
LDA calculations. These considerations are important when computing t
emperature-composition phase diagrams since formation energies of many
ordered structures are the crucial input to the calculation. We used
the CaO-MgO system as a prototype system to illustrate the effectivene
ss of the tight-binding method. We show that by fitting its parameters
to ab initio plane-wave pseudopotential calculations for a few simple
ordered structures the formation energy of more complex structures ca
n be easily predicted. We also compute the solubility limits of the Ca
O-MgO phase diagram.