Using the plane wave ultrasoft pseudopotential method based on the first-principles density functional theory(DFT),the influence on the electronic structure and dehydrogenation properties of VH2 doped with Zr,Cu and Zn has been studied.The results show that the negative heat of formation increases and the valence electron number at the Fermi level EF,N(EF) decreases in the Zr-doped model,indicating the higher stability of VH2 after Zr alloying.On the other hand,the negative heat of formation of VH2 decreases and the N(EF) increases in Cu-or Zn-doped systems,suggesting the lower stability of VH2 after Cu or Zn alloying.The calculated overlap populations and electron densities of the V-H bond demonstrate that the bonding is strengthened by Zr doping and weakened by Cu or Zn doping.The results predict that the maximum capacity to absorb and desorb hydrogen can be raised by the introduction of Zr and reduced by the introduction of Cu or Zn,while the dehydrogenation properties will be poorer in Zr-doped systems and enhanced in Cu-or Zn-doped systems.These predictions are consistent with the experimental results.Mulliken populations were also calculated and it was found that the Mulliken population of the V 3d orbitals decreased as a result of Zr doping,and increased after Cu or Zn doping.
