The importance of anharmonic effects in models that interconnect point defect parameters with bulk properties in solids

We point out that the ability of a model that interconnects the defect Gibbs energy g(i) with bulk properties to reproduce the Al self-diffusion coefficients D up to the melting point stems from the fact that it seems to capture anharmonic effects. This conforms to recent findings that, in the high temperature region, microscopic studies using density-functional theory (DFT) in combination with the quasiharmonic approximation (QHA) reveal that some thermal properties of Al cannot be fully accounted for, probably due to the anharmonic effects not included in QHA. The importance of these effects is also emerged in inelastic neutron scattering experiments, which find an almost quadratic increase in phonon linewidth with temperature. Furthermore, we discuss recent claims that DFT microscopic calculations enable the satisfactory determination of D even in the harmonic approximation.