科研之友
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摘要
The behaviors of intrinsic defects in solid molecular hydrogens (H-2) were investigated using ab initio calculations based on density functional theory. The results show that the formation energy of a vacancy is dependent on molecule orientation in disordered hexagonal close-packed (hcp) H-2 crystals, but independent of molecular orientation in face-centered cubic-Pa3 H-2. Furthermore, H-2 molecules generally prefer to occupy the basal octahedral sites in hcp and octahedral sites in Pa3 structures. The formation energies of an interstitial H-2 depend sensitively on the volume of interstitial sites, and also on near spatial distributions of molecular axes of a H-2 in hcp H-2 crystals. The strong force field introduced by an interstitial H-2 might induce the rotation of molecular axes and reduce the formation energy of the interstitial H-2. The migration barrier energy of a vacancy in Pa3 is larger than the average in hcp structures. However, the H-2 molecules prefer to jump though vacancies in the two structures of solid H-2 than the interstitial migrations.
