Abstract：Properties of various defects of He and H atoms in W–Ta alloys are investigated based on density functional theory. The tetrahedral interstitial site is the most configured site for self-interstitial He and H in W and W–Ta alloys. Only a single He atom favors a substitutional site in the presence of a nearby vacancy. However, in the coexistence of He and H atoms in the presence of the vacancy, the single H atom favors the tetrahedral interstitial site (TIS) closest to the vacancy, and the He atom takes the vacancy center. The addition of Ta can reduce the formation energy of TIS He or H defects. The substituted Ta affects the charge density distribution in the vicinity of the He atom and decreases the valence electron density of the H atoms. A strong hybridization of the H $s$ states and the nearest W $d$ state s exists in W$_{53}$He$_{1}$H$_{1}$ structure. The sequence of the He $p$ projected DOS at the Fermi energy level is in agreement with the order of the formation energy of the He–H pair in the systems.
2018, Vol. 35 
