Positron lifetime calculations of defects in vanadium containing hydrogen

Positron lifetime quantum-mechanical calculations were carried out for the investigation of defects in vanadium containing hydrogen atoms. The convergence of electronic structure calculations for supercell size is studied for vacancies, vacancy-clusters (nano-voids) and vacancy-clusters containing hydrogen. The electron wave functions have been obtained in the local density approximation (LDA) to the density functional theory (DFT). On the basis of the calculated results, the behaviours of empty nano-voids and nano-voids with hydrogen are discussed. It is found that hydrogen in larger three-dimensional vacancy-clusters change the annihilation characteristics drastically. The hydrogen atoms are trapped by lattice vacancies. These results provide physical insight for positron interactions with defects in vanadium and can be used for the prediction of hydrogen generation useful for the design of a fusion reactor.