Accurate calculation of the free energy of defects was important in understanding many mechanical processes and properties in materials. Here a method was proposed for directly calculating the free energy difference between bulk crystal and defect multi-component atomic systems. Based on λ-integration techniques it involved defining a non-physical but reversible thermodynamic pathway that connects the bulk reference crystal and defect structures. This pathway could be thought of as a so-called alchemic route to the free energy as selected atoms were allowed to transform their atomic character. The method was demonstrated by using it to calculate the free energy of Ni3Al antiphase boundaries where atomic interactions were modelled through a Finnis-Sinclair type potential.

Free Energy Calculation of Extended Defects through Simulated Alchemy: Application to Ni3Al Antiphase Boundaries. Skinner, A.J., Lill, J.V., Broughton, J.Q.: Modelling and Simulation in Materials Science and Engineering, 1995, 3[3], 359-69