Energetic, electronic and structural DFT analysis of point defects in refractory BCC metals

First wall and plasma facing materials of future fusion reactors must withstand high temperatures and intense radiation damage from impinging reaction products such as high-energy neutrons, alpha particles, X-rays and energetic ions. Those particles have a sufficient kinetic energy to knock out large numbers of lattice atoms in structural materials from their sites during the foreseen lifetime of a fusion reactor. Within this context, we have performed a systematic plane-wave density functional theory (PW-DFT) study of the stability, energetics, electronic and structural properties of vacancies, self-interstitial atoms (SIAs) and H/He impurities in the pure refractory BCC metals W, Nb, Mo, and Ta, that have been identified as possible candidates, alone or alloyed among them, for the first wall of the complete system. The standard procedures for the creation of working and transferable pseudopotentials as recommended by the literature in the field have been followed. Our original goal has been the development and testing of high-quality home-made pseudopotentials generally valid to enable the study of the behaviour of such point defects appearing in the aforementioned materials subject to irradiation by means of PW-DFT codes. Albeit the systematic approach followed and the care taken in following the methodological canon, as evidenced in the compliance of many of our results with those found in the literature, we have found some of them, and specially those concerning the behaviour of SIAs in Mo, to be controversial to the ones obtained by some authors.