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Using first-principles calculations, we predict mechanical and thermodynamic properties of both Mg17Al12and Mg2Sn precipitates in Mg–Al–Sn alloys. The elastic properties including the polycrystalline bulk modulus, shear modulus, Young’s modulus, Lame’s coefficients and Poisson’s ratio of both Mg17Al12and Mg2Sn phases are determined with the Voigt–Reuss–Hill approximation. Our results of equilibrium lattice constants agree closely with previous experimental and other theoretical results. The ductility and brittleness of the two phases are characterized with the estimation from Cauchy pressure and the value ofB/G. Mechanical anisotropy is characterized by the anisotropic factors and direction-dependent Young’s modulus. The higher Debye temperature of Mg17Al12phase means that it has a higher thermal conductivity and strength of chemical bonding relative to Mg2Sn. The anisotropic sound velocities also indicate the elastic anisotropies of both phase structures. Additionally, density of states and Mulliken population analysis are performed to reveal the bonding nature of both phases. The calculations associated with phonon properties indicate the dynamical stability of both phase structures. The temperature dependences of thermodynamic properties of the two phases are predicted via the quasi-harmonic approximation. [ABSTRACT FROM PUBLISHER]

Numerous new carbon allotropes have been uncovered by compressing carbon nanotubes based on our computational investigation. The volume compression calculations suggest that these new phases have a very high anti-compressibility with a large bulk modulus (B0). The predicted B0 of new phases is larger than that of c-BN (373 GPa) and smaller than that of diamond (453 GPa). All of the predicted structures are superhard transparent materials with a larger band gap and possess the covalent characteristics with sp3-hybridized electronic states. The simulated results will help us better understand the structural phase transition of cold-compressed carbon nanotubes. [ABSTRACT FROM AUTHOR]