放热型金属合金化对钒基贮氢材料性能影响的理论研究

Theoretical Investigation on the Effect of Exothermic Alloying on Storage Hydrogen Materials

利用电荷自洽离散变分Xα(SCC-DV-Xα)方法计算了放热型金属合金化对钒基贮氢材料性能的影响。研究结果表明:在钒氢化物V63H64中加入放热型金属后,钒原子的净电荷都减少,而氢原子的净电荷既有增加又有减少,加入Ti、Ca以后,H原子的净电荷减少,而加入Mg、Zr以后,H原子的净电荷增加。研究还表明放热型金属合金化以后,V4s轨道电子态密度峰发生分裂,与H1s和H2s轨道电子态密度重叠程度增大,V-H之间相互作用增强;差分电荷密度还表明M-H之间也有较强的相互作用。Mg合金化导致氢化物V51M12H64的费米能增加,氢化物稳定性减弱;Ca、Ti、Zr合金化导致氢化物V51M12H64的费米能减少,氢化物更稳定。

The effect of exothermic alloying on Vanadium-based hydrogen storage materials is calculated by the method of Xα （SCC-DV-Xα） cluster. The calculated results show that： when the exothermie metal is added into V63H64, the net charge of V decreases, on the other hand, the net charge of H decreases when Ti or Ca is added into V63H64, while it increases by adding of Mg or Zr into V63H64. Moreover, with the alloying of exothermie metal, the density peak of V4s orbital breaks up. And the V4s orbital overlaps with Hls and H2s more in exothermie alloyed materials than in unalloyed V63H64, which demonstrates that the ionic interaction between V and H strengthens. And, the charge density difference indicates strong interaction between the alloying metal M and H in V51M12H64. The Fermi energy of V51Mg12H64 is higher than unalloyed V63H64, which displays that the hydride becomes more unstable by adding of Mg. Oppositely, the Fermi energy of the hydride falls down by adding of Ca, Ti, Zr, thus V51M12H64（M=Ca, Ti, Zr） are more stable than unalloyed V63H64.