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 He(x)H(y) complexes in a vacancy than H atoms. (C) 2008 Elsevier B.V. All rights reserved.