Correlation between CALPHAD data and the Cahn–Hilliard gradient energy coefficient κκ and exploration into its composition dependence

Expressions for the Cahn–Hilliard gradient energy coefficient κκ for a binary, face-centered cubic crystal are derived by consideration of pair-wise, three-body, and four-body nearest-neighbor interactions. The resulting equations are expressed in terms of the interaction energies of clusters of atoms, and are related to bulk thermodynamic data available in CALPHAD databases. The three- and four-body interactions introduce a composition dependence into the expressions for κκ. Values of κκ calculated for the Al–Zn system are in good agreement with those reported elsewhere. Equilibrium composition profiles and interfacial energies are calculated using each approximation.