Trapping of helium atom by vacancy in tungsten: a density functional theory study Ningning Zhang, Yujuan Zhang, Yu Yang, Ping Zhang, Ziyu Hu and Changchun Ge Eur. Phys. J. B, 90 5 (2017) 101 Published online: 24 May 2017 DOI: 10.1140/epjb/e2017-80056-1