Invited
AB INITIO BASED MODELING OF DEFECTS IN METALS: FROM RADIATION DEFECTS TO DISLOCATIONS

Ab initio electronic structure calculations based on the Density Functional Theory (DFT) are a very powerful and versatile tool to study the structure and energetics of defects in metals. With supercells containing up to a few hundred atoms and energies corrected for elastic interactions between periodic images, defects relevant to the behavior of materials for nuclear energy can be studied, in particular the clustering of point defects formed under irradiation, being of vacancy or self-interstitial type, and the core structure of dislocations. In a multiscale modeling approach, these ab initio data are used to develop improved empirical potentials for large scale molecular dynamics simulations and as input data for kinetic model simulations.

This will be illustrated by calculations performed in body centered cubic transition metals (V, Nb, Ta, Mo, W, Fe), evidencing strongly metal-dependent properties. For self-interstitial clusters, a 3D crystalline structure, of C15 type, is predicted in Fe and Ta, as opposed to the conventional 2D loop geometry. These highly immobile clusters are important to take into account for predicting the microstructural evolution under irradiation. As for ½ screw dislocations, we find that the stable structure is always the non-degenerate easy-core configuration in pure metals, and that their strongly group-dependent core energies can be explained by defect states partially filling the pseudo-gap of the electronic density of states. Finally, the trajectory of the dislocation, which is dictated by the topology of the 2D Peierls potential, is shown to deviate significantly from the average {110} plane, giving new insight into the crystal-orientation dependence of the Peierls stress.