A density functional theory assessment of the clustering behaviour of He and H in tungsten

We have used density functional theory based ab initio calculations to investigate the tendency of He and H to form clusters. For both species the most stable interstitial configuration is in a tetrahedral site, however their clustering tendencies are totally different. The He–He interaction is purely elastic in nature and as such highly binding at close separation distances. The H–H interaction on the other hand is almost negligible since the elastic binding effect is compensated for by the change in effective position of the H states in the density of states. He atoms always bond more strongly to HexHy complexes in a vacancy than H atoms.