Relaxation of internal stress field and hydrogen ordering on YHx

Although there have been several theoretical efforts in the past to calculate both the best structure of H–H pairs in Y and the total energies as well as electronic structures, there exist no studies of the relation between hydrogen ordering and the shape of the Fermi surface. We use the FLAPW method, as implemented in the Wien2k code, focusing our research on the relation between chain ordering of H, the relaxation of internal coordinates and the electronic properties for hypothetical α-YH1/3 and α-YH2/3. In addition to the relaxed atomic positions in the cell, we obtain information on the negligible role of the H 1s state contribution near EF and the shape of the Fermi surface.