Phase diagram of an empirical potential: The case of Fe-Cu

Molecular dynamics simulations are used to calculate the Gibbs free energy in the entire compositional range of Fe-Cu alloys described with a set of embedded atom potentials available in the literature. Thermodynamic integration and switching Hamiltonian techniques are used to obtain the phase diagram at high temperatures (neglecting phonon quantum effects and electronic contributions) with no further approximations. Limitations of the model were confirmed, such as the absence of the {γ} and {δ} phases, a bcc to fcc transformation before melting for pure Fe, the unexpected existence of a stable bcc phase in pure Cu at high $T,$ and consequently complete solid solubility of Fe in Cu in the bcc phase in some temperature range. This work seeds light on the power and limitations of the empirical description of complex systems.