The diffusion of point defects produced by irradia­tion may induce fluxes of solutes, for example, toward
or away from defect sinks, depending on the defect — solute interactions. DFT is again a very powerful tool to predict such interactions, which can then be used in kinetic models. This approach is also useful in the absence of irradiation, and a very interesting example has been obtained in the simulation of the first stages of the coherent precipitation of copper in bcc-Fe. DFT calculations predicted that the vacancy — formation energy in metastable bcc-Cu (which is not known experimentally since bulk Cu is fcc) is 0.9 eV, that is, much smaller than that in bcc iron, namely 2.1 eV. This leads to strong trapping of vacan­cies by the Cu precipitates. As a result, precipitates containing up to several tens of copper atoms are quite surprisingly predicted to be much more mobile than individual copper atoms in the iron matrix.26 Another very illustrative example is given by the study of atomic transport via interstitials in dilute Fe-P alloys. DFT results indeed predict that Fe-P mixed dumbbells are highly mobile but that they can be deeply trapped by a substitutional P atom.79 A systematic study of the interaction of monovacan­cies and self-interstitials with all transition-metal solutes has been reported recently (see Figure 8).80