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We present an unbiased structure search for shape memory alloy NbRu using the particle swarm optimization algorithms combined with first-principle calculations. Based on our search, two experimentally observed cubic P m 3 ¯ m and tetragonal P 4/ mmm structures are successfully reproduced under ambient pressure conditions. We confirmed the middle transition phase β” (orthorhombic or monoclinic) observed in experiment belongs to orthorhombic Pnma structure. By calculating the formation enthalpies under high pressure up to 100 GPa, it is found that tetragonal P 4/ mmm structure has potential for application under high pressure. Additionally, high-pressure phase transition is identified between cubic P m 3 ¯ m structure and the orthorhombic Pnma structure at 50 GPa, above which, the orthorhombic Pnma phase is more energetically favorable. The analysis of density of states shows that all the studied NbRu structures exhibit metallic behavior and the d orbitals of both metal compositions Nb and Ru play important role.

The structural, elastic, mechanical, electronic properties and its compressive behavior up to 55 GPa are studied for the (Ti1−xNbx)2AlC (x = 0, 0.25, 0.5, 0.75, 1.0) compounds using the first-principles calculation. Calculated structural parameters are in good agreement with experimental results, and all the considered (Ti1−xNbx)2AlC compounds are predicted to be elastically stable under 0–55 GPa pressure and are classified as brittle materials. Meanwhile, our study provides a metallic character of all the considered (Ti1−xNbx)2AlC compounds, and predicts them as promising good coating materials. Moreover, a significant increase (25.8%) in the bulk modulus is found with the Nb concentration changing from 0 to 1.0, and the reason is analyzed.

We have carried out a systematic study on the structural phase transition, elastic properties and hardness of B31 and B20-phase RhSi under high pressure by first-principles calculations using the pseudopotential plane-wave method. The calculated values at zero pressure are in good agreement with experiments and similar theoretical calculations. Among them, the mechanism of the high pressure induced structural phase transition of RhSi has been studied in a detailed fashion. Under compression, the theoretical calculations show that RhSi will undergo a structural phase transition from B31-phase to B20-phase at 5.59 GPa. Based on the semiempirical method of the evaluation of covalent crystal, the hardness Hν of RhSi is estimated under high pressure. Remarkably, the theoretical results suggest that at zero pressure, the hardness value of B31-RhSi is 14.8 GPa and that of B20-RhSi is 19.0 GPa.

A systematic study of the structural stability, elastic properties and electronic structures for iridium silicide (IrSi) in B31 and B20-phase has been carried out with the generalized gradient approximation (GGA) and local density approximation (LDA) in framework of density functional theory (DFT). The obtained formation enthalpies, energy–volume (E–V) curves and enthalpy–pressure (H–P) curves indicate that orthorhombic B31-IrSi is more stable than cubic B20-IrSi at both ambient and pressure conditions. The elastic stiffness constants, bulk moduli, shear moduli, Young’s moduli, Poisson’s coefficients and elastic anisotropy factors of the two phases IrSi are studied for the first time. The small elastic stiffness constant C22 of B31-IrSi induces easily compressibility along the b axis. Moreover, based on the Mulliken overlap population analysis, the hardness Hv of B31-IrSi (Hv = 11.9 GPa) and B20-IrSi (Hv = 13.4 GPa) are evaluated.

According to the new experimentally discovered Cr 2 (Al x Ge 1− x )C ( x = 0, 0.25, 0.5, 0.75, 1) alloys, we have studied the structural, mechanical, electronic and optical properties based on the first-principles calculation. Obtained structural parameters and distortion parameters are in good agreement with experimental results. It is shown that all the considered compounds are elastically stable and present results classify the Cr 2 (Al x Ge 1− x )C ( x ⩽ 0.5) alloys as ductile while the Cr 2 (Al 0.75 Ge 0.25 )C and Cr 2 AlC as brittle. Electronic and optical properties demonstrate that all the considered M 2 AX compounds have a metallic character, and they are predictive of promising good coating materials.

Using first-principles calculations, the elastic constants, thermodynamic property and structural phase transition of rhenium diboride under pressure are investigated by means of the pseudopotential plane-waves method, as well as the effect of metallic bond on its hardness. Eight candidate structures of known transition-metal compounds are chosen to probe for rhenium diboride ReB2. The calculated lattice parameters are consistent with the experimental and theoretical values. Based on the third order Birch–Murnaghan equation of states, the transition pressure Pt between the ReB2–ReB2 and MoB2–ReB2 phases is firstly determinate. Elastic constants, shear modulus, Young’s modulus, Poisson’s ratio and Debye temperature are derived. The single-bonded B–B feather remains in ReB2 compounds. Furthermore, according to Mulliken overlap population analysis, a semiempirical method to evaluate the hardness of multicomponent crystals with partial metallic bond is presented. Both strong covalency and a zigzag topology of interconnected bonds underlie the ultraincompressibilities. In addition, the superior performance and large hardness (39.1 GPa) of ReB2–ReB2 indicate that it is a superhard material.

For a d(3) configuration ion, the 120 x 120 complete energy matrix which contains the electron-electron repulsion interaction, the ligand field interaction, the spin-orbit coupling interaction as well as the Zeeman interaction, has been established. By diagonalizing the complete energy matrix, local structure and EPR g factors for Cr3+ ions doped in KA1(MoO4)(2) and RbIn(MoO4)(2) have been investigated, respectively. It is found that the orbit reduction effect is very important to understand the EPR g factors for Cr3+ ions doped in KA1(MoO4)(2) and RbIn(MoO4)(2), and some characteristics of orbit reduction on the EPR g factors are discussed firstly. Simultaneously, by simulating the calculated optical spectra and the EPR spectra data to the experimental results, we obtain the local structure parameters R = 2.043 angstrom, theta = 53.5940 degrees and R = 2.065 angstrom, theta = 56.0434 degrees for Cr3+ ions doped in KA1(MoO4)(2) and RbIn(MoO4)(2), respectively. The calculated results show the local lattice structure of the octahedral Cr3+ centers in KA1(MoO4)(2) and RbIn(MoO4)(2) exhibit an elongation and a compression distortions, respectively. (c) 2006 Elsevier B.V. All rights reserved.