First Principles Calculations of Phase Stabilities of MgH2 and Mg7XH16(X=Nb,V,Ti)

First-principles calculations were performed to study the relative stabilities of MgH2 and Mg7XH16(X=Nb,V,Ti).The calculated results show that MgH2 has the higher stability than Mg7XH16. The density of states of MgH2 and Mg7XH16 were obtained and analysized. It shows that the extinction of the gap at 0~4eV interval , the increment of N(EF) and the weakening of Mg-H bonds impaired the stability of Mg7XH16.