The elastic property and electronic structure of three typical Al–Ce structures have been studied by means of first-principles calculations within GGA approximation. The optimized structural parameters for these precipitates agree very well with experimental data. The obtained negative cohesive energy and formation enthalpy show that all of these precipitates have strong structural stability. Elastic constants as well as other mechanical parameters such as bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν for these phases are computed and discussed. The calculated electronic densities of state and charge distribution show the covalent features of Ce–Ce and Al–Ce bonding in three phases, which reveals the underlying mechanism for the elastic properties of these Al–Ce structures.

The product rotational polarization in the Ca + HCl→CaCl + H reaction at collision energy of 20 kcal/mol has been studied via the quasiclassical trajectory method on a new ab initio potential surface. The P(θ r ) distribution of angle between k and j′, and the dihedral angular distribution P(Φ r ) characterizing k - k′ - j′ correlation are discussed, the angle distribution P(θ r , Φ r ) of product rotational vectors in the form of polar plot in θ r and Φ r are shown. Furthermore, four PDDCSs (2π/σ)(dσ00/dωt), (2π/σ)(dσ20/dωt), (2π/σ)(dσ22+/dωt) and (2π/σ)(dσ21-/dωt) are also presented. The present calculations reveal that the product rotational alignment is very strong. Finally, the state distributions of the product CaCl are investigated. The results showed that the CaCl product was formed with high vibrational and rotational excitation.

The first-principles calculation based on density functional theory has been carried out to study the microstructural feature of the novel 24R-type long period stacking ordered structure in Mg97Zn1Y2 alloy. The lattice positions of the Y and Zn atoms are determined theoretically, it is shown that the additive atoms are firstly enriched in the stacking fault layers at the two ends, a small amount are distributed in the interior stacking fault layers of the structure. And the arrangement of these Y and Zn atoms trends to be along the diagonal line of the unit cell. The structural stability is analyzed and the electronic density of state is discussed as well as.

The crystal structure of the 10H-type long-period stacking order structure in Mg-Y-Zn alloy was investigated by first-principle calculations. The calculated results show that the accurate positions and distinctive arrangement of Zn and Y atoms in the most stable 10H-type LPSO phase exhibit mirror symmetry with respect to the atomic layer C-6. which agrees well with the experimental observations. Theoretical calculations still indicate that the mirror symmetry 10H-type ABACBCBCAB phase is not distorted, the lattice distortion of other LPSO phases may originate from the asymmetry of Zn element in the chemical order and stacking order. The obtained electronic density of states (DOS) reveals the underlying mechanism for mirror symmetry of 10H-LPSO phase. (C) 2010 Elsevier B.V. All rights reserved.

Ab initio density functional theory (OFT) and density function perturbation theory (DEPT) have been used to investigate the thermal properties of the Al-Mg-Sc, Al-Mg-Zr and Al-Mg-Sc-Zr alloys over a wide range of temperature and pressure. Phonon dispersions are obtained at equilibrium and strained configurations by DEPT. Using the quasiharmonic approximation (QHA) for the free energy, several physical quantities of interest such as thermal Gruneisen parameter, heat capacity at constant pressure and at constant volume, thermal expansion coefficient, entropy, adiabatic bulk modulus and isothermal bulk modulus as a function of temperature and pressure are calculated and discussed. The present results show that the thermal expansion coefficient of the Al-Mg-Sc-Zr is far lower than that of Al-Mg-Sc and Al-Mg-Zr, and the variation features in the adiabatic bulk modulus and isothermal bulk modulus for the Al-Mg-Sc-Zr are also very different from that of Al-Mg-Sc and Al-Mg-Zr. (C) 2010 Elsevier Masson SAS. All rights reserved.

Ab inito density functional theory (DFT) and density function perturbation theory (DFPT) have been applied to investigate the thermal properties of the face-center-cubic (fcc) Al3Zr alloy over a wide range of pressure and temperature. Phonon dispersions were obtained at equilibrium and strained configurations by density functional perturbation theory. Using the quasiharmonic approximation for the free energy, several interesting physical quantities such as thermal Grüneisen parameter, heat capacity at constant pressure and volume, thermal expansion coefficient and entropy, as well as adiabatic bulk modulus and isothermal bulk modulus, were calculated as a function of temperature and pressure, and the variation features of these quantities were discussed in details.

We have performed a first-principles calculation within the generalized gradient approximation to investigate the β″ phase in Mg–Gd alloy system. The lattice parameters are determined theoretically by structural optimization of full relaxation and the β″ phase Mg3Gd is found to be energetically favorable from the calculated formation enthalpy. The nine independent elastic constants are calculated, indicating the proposed Mg3Gd structure is mechanically stable. Then the polycrystalline bulk modulus B, shear modulus G, Young's modulus E and Poisson ratio ν are gained by the Voigt–Reuss–Hill (VRH) approximation. The elastic anisotropy is discussed in detail. The electronic density of states and charge density distribution are analyzed, indicating the existence of covalent bonding in Mg3Gd. The Debye temperature is also estimated for the investigation in the future.

The β′ phase precipitate in Mg–Gd alloy system has been investigated by means of first-principles calculation within the generalized gradient approximation. The lattice parameters are determined theoretically by structural optimization of full relaxation, and the Mg7Gd is found to be energetically more stable compared with the Mg15Gd from the calculated formation energy. The nine independent elastic constants are calculated, indicating the proposed Mg15Gd structure in literature is mechanically unstable. Then the polycrystalline bulk modulus B, Young's modulus E, shear modulus G, Poisson ratio ν of Mg7Gd are gained by the Voigt–Reuss–Hill (VRH) approximation. The ductility and plasticity, especially elastic anisotropy are discussed in details. Based on the electronic density of states and charge density distribution, the covalent bonding and metallic bonding are exhibited in Mg7Gd compound. Last, the Debye temperature is also calculated for the investigation in the future.

Ab initio density functional theory (DFT) and density function perturbation theory (DFPT) have been used to investigate the thermal properties of the fcc Al3Mg and Al3Sc alloys over a wide range of pressure and temperature, in comparison with fcc Al. Phonon dispersions were obtained at equilibrium and strained configurations by density functional perturbation theory. Using the quasiharmonic approximation for the free energy, several thermal quantities of interest, such as the thermal Grüneisen parameter, heat capacity, thermal expansion coefficient and entropy, were calculated as a function of temperature and pressure, and the variation features of these quantities were discussed in detail. This investigation provides useful information for design and applications of technologically relevant Al-based alloys.

Microstructure and electronic characteristics of the 6H-type ABACAB LPSO structure in Mg97Zn1Y2 alloy are investigated by means of first-principles calculation within the generalized gradient approximation. The accurate positions of the solid solution atoms Y and Zn together with the arrangement rules are determined theoretically and the lattice distortion of the 6H-type ABACAB structure is also discussed in comparison with the 6H-type ABCBCB′ structure. The stability is also analyzed on the basis of the calculated cohesive energy, which reveals that Y element stabilizes the structure significantly. The electronic characteristics show that the Y element enhances the strength of alloy due to the presence of Mg–Y covalent bonding and the hybridization between Mg and Zn is relatively strong in entire region which contributes to improve the alloy's ductility.

Based on first-principles calculations, we have investigated the elastic properties and electronic structure of a new MAX compound (Cr0.5V 0.5)2GeC. The obtained lattice parameters agree very well with available experimental and theoretical data. Elastic constants are calculated, then the mechanical properties such as compressibility, ductility and stiffness, especially elastic anisotropy of (Cr0.5V 0.5)2GeC are discussed in detail. The calculated charge density and density of state exhibit a mixture of covalent and ionic features in (Cr0.5V 0.5)2GeC due to the strong hybridization of C 2p with Cr 5d and V 4d states. The coexistence of the stronger and stiffer Cr–C and V–C covalent bonds reveals the underlying mechanism for the higher bulk modulus of (Cr0.5V 0.5)2GeC.