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We investigate the elastic properties, lattice dynamical, thermal equation of state and thermodynamic properties of bcc phase W under high pressure using density functional theory. The calculated high-pressure elastic constants of bcc phase W agree well with experimental and theoretical data. Under compression, the phonon dispersion curves of bcc phase W do not show any anomaly or instability. Our calculated zero-pressure phonon dispersion curves are in excellent agreement with experiments. Within the quasiharmonic approximation, we predict the thermal equation of state and other properties including the thermal expansion coefficient, adiabatic bulk modulus, specific heat at constant volume and entropy. [ABSTRACT FROM AUTHOR]

The study aims at the elastic, mechanical, electronic properties and hardness of Nb2AsC using first principles based on the density functional theory method within the generalised gradient approximation. The calculated lattice parameters of Nb2AsC are in good agreement with the experimental data. The five independent elastic constants are firstly calculated as a function of pressure, and our results indicate that it is mechanically stable in the applied pressure. The elastic anisotropy is examined through the computation of the direction dependence of Young's modulus. The pressure dependences of the bulk modulus, shear modulus, average velocity of acoustic waves and Debye temperature of Nb2AsC are systematically investigated. The band structure and density of states are discussed, and the results show that the strong hybridisations Cp–Nbdand Asp–Nbdwould be beneficial to the structure stability of Nb2AsC. Based on the Mulliken population analysis, the hardness of Nb2AsC is predicted. [ABSTRACT FROM AUTHOR]

The temperature-dependent elastic constants of body-centred cubic (bcc) phase W are presented from first principles quasi-static approach. With the quasi-harmonic approximation model, the Hugoniot equation of state and temperature-dependence linear thermal expansion coefficient is successfully obtained. The adiabatic elastic constants show a normal behaviour with temperature: decrease with increasing temperature. Based on the obtained adiabatic elastic constants, the structural stability and polycrystalline aggregate properties including bulk modulusB, shear modulusG, andB/Gratio are analysed for bcc phase W. In addition, the sound velocities as a function of temperature for bcc phase W are predicted. [ABSTRACT FROM AUTHOR]

The elastic constants and the elastic anisotropy in hexagonal close-packed Fe–Ni alloys have been investigated at high pressures by plane-wave density functional calculations within the generalized gradient approximation and the Monte Carlo special quasi-random structure method. The comparisons with previous calculations and experiments are shown and discussed. We find that adding Ni to Fe has a certain influence on the structure and elasticity of hexagonal close-packed Fe–Ni alloys generally. In particular, the elastic constant C 44 is seriously affected by the increasing Ni content. Furthermore, the elastic moduli and wave velocities yielded from disordered structures are slightly greater than those from the ordered structures in previous calculations at high pressures. Interestingly, the elastic anisotropies of the compressional wave are close to 1.1 and there are small changes with increasing pressure and Ni content, which indicates that the anisotropies are little affected by pressures and Ni content within disordered structure. • Most elastic data of the disordered systems are slightly greater than the ordered results from previous calculations. • Elastic anisotropy of the compressional wave is little affected by pressures and Ni content within disordered structure. • MCSQS method is used to generate the disordered structure of Fe–Ni alloys. [ABSTRACT FROM AUTHOR]

In this paper, we searched the high-pressure structure of metal Ru with the advanced crystal structure prediction algorithm combined with the density functional theory (DFT). We discovered two experimentally unknown structures, the face-centered-cubic (fcc) and the structure with the R 3 ̄ m symmetry, except for the known hexagonal-closely-packaged (hcp) structure. We constructed a wide-range high-pressure and temperature phase diagram of Ru from ambient conditions up to 500 GPa and 10,000 K based on the quasi-harmonic approximation (QHA). The dynamic Hugoniot equation of states of Ru was investigated for the first time, which shows a slight mismatch between hcp and fcc on their phase boundary. Finally, using the stress–strain method we verified the previous high-pressure elastic constants calculated by the energy–strain method. Furthermore, we analyzed the variations of the elastic moduli, elastic anisotropy, sound velocities, and Debye temperature with pressure. • We discovered two experimentally unknown structures of Ru. • We constructed its wide-range high-pressure and temperature phase diagram. • The dynamic Hugoniot equation of states of Ru are investigated for the first time. • We addressed the elastic anisotropy of Ru using our proposed stress–strain method. [ABSTRACT FROM AUTHOR]