Elastic Properties Of Hcp Lithium And Hydrogen Doped Lithium Under Pressure

This paper presents ab initio studies on the system of hcp lithium doped by hydrogen atom, for understanding the role how impurity and external pressure influence the elastic properties of metal lithium. By applying deformations, total energy and elastic constants can be obtained by optimizations. Here six strain models and a maximum strain of 0.0005 are used. The elastic constants are derived from the relations between the stress and the strain using linear fitting algorithm. The elastic constants of pure lithium are calculated using the primitive cell of hexagonal closed-pack (hcp) lattice including two atoms. The results show that C 12 and C 13 increase linearly with the pressure, C 44 and C 66 are insensitive to the pressure. At about 3GPa C 11 and C 33 have step changes , corresponding to the behavior of electrons on the Fermi surface. Hcp lithium have compressional elastic isotropy and shear elastic anisotropy. Under ambient pressure Cauchy ratios and the normalized elastic constants of lithium behaves as those of some transition metals. Cauchy violation "3C 12 ? C11?2P"increases linearly with pressure, and "C 13 ? C44?2P"is insensitive to pressure. A supercell including 16 lithium atoms in hcp lattice is constructed with a hydrogen atom doped in. After zero temperature geometry optimization, the equilibrate structure belongs to C2/M and P-3M1 symmetry depends on the high/low accuracy, respectively. For the computational efficiency and the comparison with the pure hcp lithium, P-3M1 symmetry is imposed. The bulk modulus increases with pressure and remains larger than that of the pure lithium under the same pressure. All the elastic constants...