Energetics of small helium clusters near tungsten surface by ab initio calculations

Density functional theory calculations have been performed to study the stability and the interactions of/between small helium clusters at the W(001) surface. Among the studied He clusters, all the He atoms prefer to stay under the second atomic layer from the surface, instead of surface and subsurface. Trapping of multiple He in tungsten surface can induce formation of a new vacancy at nearby lattice site , and the He n -V (n = 2 and 3) complexes are formed concurrently. The electronic densities of states (DOS) and charge-density distribution are presented for di-helium and tri-helium clusters. Calculated He formation energies and He-vacancy binding energies improve understanding of He trapping behavior and diffusion mechanisms in tungsten surface.