First-principles investigations on structural,elastic and electronic properties of SnO2 under pressure

We investigate the structural, elastic, and electronic properties of rutile-type SnO₂ by plane-wave pseudopotential density functional theory method. The lattice constants, bulk modulus and its pressure derivative are all calculated. These properties at equilibrium phase are well consistent with the available experimental and theoretical data. Especially, we study the pressure dependence of elastic properties such as the elastic constants, elastic anisotropy, aggregate acoustic velocities and elastic Debye temperature Θ. It is concluded that this structure becomes more ductile with increasing pressure up to 28 GPa. Moreover, our compressional and shear wave velocities V_P = 7.02 km/s and V_S = 3.84 km/s, as well as elastic Debye temperature Θ = 563 K at 0 GPa compare favorably with the experimental values. The pressure dependences of band structures, energy gap and density of states are also investigated.     

First-principles study of structural and elastic properties of MgSe under hydrostatic pressure

The structural and elastic properties were calculated using ab initio plane wave pseudopotential method within the generalized gradient approximation (GGA). Our results indicated that MgSe undergoes a structural phase transition from NaCl-type (B1) to FeSi-type (B28) at a pressure near to about 111 GPa. The calculated elastic stiffness coefficients presented a linear behaviour versus pressure. The structural parameters and elastic constants of the fundamental ground are generally in good agreement with the available theoretical and experimental data.     

First-principles study of the structural,elastic and electronic properties of HfTaO3N

HfTaO₃N is an important material in the future industrial applications. However, there are no data in the literature about these analysis. In this paper, structural parameters, elastic, electronic and bonding properties of HfTaO₃N have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). These properties of HfTaO₃N have been firstly theoretically predicted, which await experimental confirmation.     

First-principles study of structural stabilities,elastic and electronic properties of transition metal monocarbides (TMCs) and mononitrides (TMNs)

The structural stabilities, elastic and electronic properties of 5d transition metal mononitrides (TMNs) XN with (X = Ir, Os, Re, W and Ta) and 5d transition metal monocarbides (TMCs) XC with (X = Ir, Os, Re and Ta) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the local density approximation (LDA) for the exchange correlation functional. The ground state quantities such as the lattice parameter, bulks modulus and its pressure derivatives for the six considered crystal structures, Rock-salt (B1), CsCl (B2), zinc-blend (B3), Wurtzite (B4), NiAs (B8₁) and the tungsten carbides (B_h) are calculated. The elastic constants of TMNs and TMCs compounds in its different stable phases are determined by using the total energy variation with strain technique. The elastic modulus for polycrystalline materials, shear modulus (G), Young's modulus (E), and Poisson's ratio (ν) are calculated. The Debye temperature (θ_D) and sound velocities (v_m) were also derived from the obtained elastic modulus. The analysis of the hardness of the herein studied compounds classifies OsN – (B4 et B8₁), ReN – (B8₁), WN – (B8₁) and OsC – (B8₁) as superhard materials. Our results for the band structure and densities of states (DOS), show that TMNs and TMCs compounds in theirs energetically and mechanically stable phase has metallic characteristic with strong covalent nature Metal–Nonmetal elements.     

First-principles calculations of structural,elastic and electronic properties of TaB2 with AlB2 structure under high pressure

We present a systematic theoretical study for the structural, elastic and electronic properties of TaB₂ with AlB₂ structure under pressures ranging from 0 GPa to 120 GPa within the framework of density-functional theory in this paper. The results at zero pressure are in good agreement with available theoretical and experimental values. Our attention has been focused on high pressure behavior of TaB₂. The pressure dependence of structure, elastic constants, Debye temperature, and density of states (DOS) are successfully calculated and discussed.     

First-principles study of structural,elastic, electronic and optical properties of orthorhombic NaAlF4

We have performed the ab initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study the structural parameters, elastic, electronic, chemical bonding and optical properties of orthorhombic NaAlF₄. The calculated lattice parameters are in good agreement with experimental work. The bulk, shear and Young’s modulus, Poisson’s coefficient, compressibility and Lamé’s constants are firstly obtained using Voigt–Reuss–Hill method and the Debye temperature is estimated using Debye-Grüneisen model. Band structure shows a direct band gap at Γ point. Density of states and charge density have been studied, which show the bonding between Na and F is mainly ionic as well as that between Al and F. In order to clarify the mechanism of optical transitions of orthorhombic NaAlF₄, the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated. The optical properties and origins of the structure have been analysed.     

Structural,electronic, elastic properties and stabilities of hexagonal ZrNiAl alloy and its hydride ZrNiAlH0.67 under pressure

The structural, electronic, elastic properties and stabilities of hexagonal prototype alloy ZrNiAl and its saturated hydride ZrNiAlH_0.67 are investigated using the pseudopotential plane wave method within the generalized gradient approximation (GGA). The calculated structural parameters are in good agreement with the available experimental data. Partial covalent characters on ZrNiAl and ZrNiAlH_0.67 are verified by the calculations of PDOS (partial density of states) and overlap population. Band structures show both ZrNiAl and ZrNiAlH_0.67 belong to metals. The elastic constants and their pressure dependences are calculated using the static finite strain technique. From the analysis of the mechanical stabilities, hexagonal ZrNiAl is unstable at higher pressure than 29.34 GPa; that its hydride ZrNiAlH_0.67 is stable up to 50 GPa is similar with the experimental result of isostructural LaNiInD_1.63−x. Hydrogenation not only leads to strong lattice anisotropy but also leads to strong mechanical anisotropy.     

First-principles study of structural, elastic, electronic, and thermal properties of LaAlO3 perovskite

In this paper, we study the structural, elastic and electronic properties of perovskite LaAlO₃ using two different methods: the full-potential linearized augmented plane wave (FP-LAPW) method and the pseudopotential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA). We have evaluated the ground-state quantities such as lattice parameter, bulk modulus and its pressure derivative as well as the elastic constants. Also, we have presented the results of the band structure, densities of states and charge densities. These results were in favourable agreement with previous theoretical works and the existing experimental data. To complete the fundamental characteristics of this compound we have analyzed the thermodynamic properties using the quasi-harmonic Debye model.     

First-principles calculations of the structural and elastic properties of OsSi2 at high pressure

We investigated the pressure dependence of the structural and elastic properties of OsSi₂ in the range 0–60 GPa using first-principles calculations based on density functional theory. Calculations were performed within the local density approximation as well as the generalized gradient approximation to the exchange correlation potential. The calculated lattice constants and atomic fractional coordinates are in good agreement with previous experimental results. The pressure dependence of nine independent elastic constants, c₁₁, c₂₂, c₃₃, c₄₄, c₅₅, c₆₆, c₁₂, c₁₃, and c₂₃, of orthorhombic OsSi₂ has been evaluated. The isotropic bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, elastic anisotropy, and Debye temperature of polycrystalline OsSi₂ under pressure are also presented.     

First-principles study of silicon nanocrystals: structural and electronic properties, absorption, emission, and doping

Total energy calculations within the Density Functional Theory have been carried out in order to investigate the structural, electronic, and optical properties of un-doped and doped silicon nanostructures of different size and different surface terminations. In particular the effects induced by the creation of an electron-hole pair on the properties of hydrogenated silicon nanoclusters as a function of dimension are discussed in detail showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure by an electronic excitation of the cluster is analyzed and considered in the evaluation of the Stokes shift between absorption and emission energies. Besides we show how many-body effects crucially modify the absorption and emission spectra of the silicon nanocrystals. Starting from the hydrogenated clusters, different Si/O bonding at the cluster surface have been considered. We found that the presence of a Si--O--Si bridge bond originates significative excitonic luminescence features in the near-visible range. Concerning the doping, we consider B and P single- and co-doped Si nanoclusters. The neutral impurities formation energies are calculated and their dependence on the impurity position within the nanocrystal is discussed. In the case of co-doping the formation energy is strongly reduced, favoring this process with respect to the single doping. Moreover the band gap and the optical threshold are clearly red-shifted with respect to that of the pure crystals showing the possibility of an impurity based engineering of the absorption and luminescence properties of Si nanocrystals.     

First principles study of structural,electronic and elastic properties of lutatium mono-pnictides

The structural, electronic, elastic and thermal properties of two lutatium mono-pnictides (LuAs and LuSb) have been studied using the density functional theory within the generalized gradient approximation. The calculations indicate that there is a structural phase transition from their ambient NaCl – (B₁) to CsCl – (B₂) structure at 56.7 and 25.2 GPa along with the volume collapse percentage of 3% and 5%, respectively. Structural parameters like lattice constant (a₀), bulk modulus (B) and pressure derivative of the bulk modulus (B′) are presented. The calculated band structures indicate that B₁ and B₂ phase of these compounds are metallic. We have calculated the second order elastic constants for these compounds. We also compare the ground state (a₀ and B) and high pressure phase transition (P_t) properties for three members of lanthanide series.     

A density functional study of structural and elastic properties of LaN under high pressure

Structural and elastic properties of LaN at normal and high pressures are investigated using ab initio calculations based on full-potential linearized augmented plane wave (FP-LAPW) within both local density approximation (LDA) and generalized gradient approximation (GGA). Our results concerning equilibrium lattice parameter and bulk modulus agree well with the available experimental and previous theoretical findings. The transition pressure from NaCl (B1) to CsCl (B2) phase is found to be 31.05 GPa from LDA, and 42.2 GPa from GGA. To the best of our knowledge, the elastic properties for LaN in the B1 structure in the presence of pressure have never been reported so far. The linear pressure coefficients of elastic constants and their related bulk modulus are determined from the pressure dependence of these parameters. Furthermore, the mechanical stability criteria for LaN in B1 phase are found to be fulfilled at normal conditions.     

Structural stabilities, electronic and optical properties of CaF2 under high pressure: A first-principles study

The structural stabilities, electronic and optical properties, the pressure-induced metallization for CaF₂ have been studied by using the density functional theory calculations. The ground phase is predicted to transform into Pnma structure at 8.1 GPa, which is well consistent with the experimental findings. Above 278 GPa, Pnma-CaF₂ transform into P6₃/mmc phase. The calculated structural data for and pnma phases are in very good agreement with experimental values. The electronic band structures show that Pnma and P6₃/mmc phases of CaF₂ are insulators at the transition pressure. Upon further compression, the band gap of P6₃/mmc decreases with pressure, and CaF₂ is predicted to undergo metallization around 2250 GPa. The possible reason for the metallization was discussed. All CaF₂ polymorphs have ionic character between Ca–F bond with the analysis of the charge–density distribution and density of states.     

First-principles calculations of structural, electronic, and elastic properties of MgZrSi2O7

For the first time, the recently synthesized pyrochlore MgZrSi₂O₇ [J. Xu et al., Mater. Chem. Phys. 128 (2011) 410] has been analyzed using the first principles calculations. The electronic and elastic properties were predicted; in particular, the band gap is indirect and has the value of 6.75 eV. The bulk modulus equals to 186.51 ± 1.95 GPa. Anisotropy of elastic properties was analyzed by comparing the upper and lower estimates of the shear moduli. In addition, directional dependence of the Young's modulus was calculated and visualized; its value varies in the range from 249.7 GPa (along the a, b, c crystallographic axes) to 136.84 GPa (along the bisector direction in any of the ab, bc, ac planes).     

The electronic, elastic and structural properties of Pd-Zr intermetallic

A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the energetic, electronic structures and elastic properties of intermetallic compounds of Pd-Zr system. The Enthalpies of formation, the cohesive energies and elastic constants of these compounds were estimated from the electronic structure calculations and their structural stability was also analyzed. The results show that the PdZr₂ compound is stable, relative to other compounds, and as the concentration of Pd increases, the enthalpy of formation gradually increased except Pd₄Zr_3.The calculated elastic constants are then used to estimate mechanical properties of Pd-Zr intermetallics compounds. The brittle/ductile behavior is assessed by analyzing the phenomenological formula G/B of shear modulus (G) over bulk modulus (B). The new knowledge from this study could be used for future development of Pd-Zr system.     

First-principles calculations on structural,magnetic and electronic properties of oxygen doped BiF3

First-principles calculations based on density function theory within the generalized gradient approximation (GGA) have been carried out to investigate the effects of O doping on the structural, magnetic and electronic properties of BiF₃. Based on the calculated cohesive energies, O impurities prefer substituting F atom at tetrahedral sites (0.25, 0.25, 0.25). And the geometry of BiF₃ changes little due to similar radius of O and F atoms. By analyzing density of states (DOS) of Bi₄OF₁₁ (II)_, it has been found that Bi₄OF₁₁ (II) presents magnetic character and half-metallic state, implying its potential applications in Li-ion batteries. Finally, the character of bond in Bi₄OF₁₁ (II) was discussed by analysis of charge density and bader charge. The result shows that O doping weakens ionic bond in BiF₃.     

First-principles study on electronic properties of SiC nanoribbon

Under the generalized gradient approximation (GGA), the electronic properties are studied for SiC nanoribbon with zigzag edge (ZSiCNR) and armchair edge (ASiCNR) by using the first-principles projector-augmented wave (PAW) potential within the density function theory (DFT) framework. Distinct variation behaviors in band gap are exhibited with increasing ribbon width. The ZSiCNR is metallic except for the thinner ribbons (N _z = 2–4) with small direct band gaps, while the direct band gaps of ASiCNR exhibit sawtooth-like periodic oscillation features and quench to a constant value of 2.359 eV as width N _a increases. The PDOS onto individual atom shows that a sharp peak appeared at the Fermi level for broader ZSiCNR comes from the edge C and Si atoms with H terminations. The charge density contours analysis shows the valence charges are strongly accumulated around C atom, reflecting a significant electron transfer from Si atom to C atom and thus an ionic binding feature. In addition, the Si–H bond is also ionic bond while the C–H bond is covalent bond. The dangling bonds give rise to one (two) flat extra band at the Fermi level for ZSiCNR with either bare C or bare Si edge (for ZSiCNR with bare C and Si edges as well as for ASiCNR with either bare C edge or bare Si edge), except for ASiCNR with bare C and Si edges in which two nearly flat extra bands appear up and below the Fermi level.     

A first-principles study on the structural, elastic, electronic, and optical properties of CdRh2O4

The structural, elastic, electronic, and optical properties of CdRh₂O₄ with cubic $ (Fd\overline{ 3} m) $ and orthorhombic (Pnma) structures have been investigated using a pseudopotential plane wave (PP-PW) method within the local density approximation (LDA). The calculated lattice parameters agree reasonably with the experimental values. The single-crystal elastic stiffness constants C _ij s of the cubic and orthorhombic phases are investigated using the stress–strain method. In addition, the polycrystalline elastic properties including bulk modulus, shear modulus, Young’s modulus, bulk modulus–shear modulus ratio, Poisson’s ratio, and elastic anisotropy ratio are determined based on Voigt–Reuss–Hill approach. The use of the hybrid functional sX-LDA leads to considerably improved electronic properties compared to standard LDA approach. On the other hand, the dielectric function, refraction index, reflectivity, conductivity function, and energy-loss spectra were obtained and analyzed on the basis of electronic band structures and density of states.     

First-principles study of the electronic,optical and bonding properties in dolomite

The structural, electronic, optical properties and chemical bonding of dolomite CaMg(CO₃)₂ (rhombohedral calcite-type structure) are investigated using plane wave pseudopotential density-functional theory (DFT) method taking the local density approximation (LDA) and the generalized gradient approximation (GGA) as the exchange–correlation energy functional. The structural properties are consistent with the early experimental and theoretical results. The indirect electronic band gap is estimated to be ～5.0 eV, which is less than the optical band gap measured from the fundamental absorption edge of ～6.0 eV. The optical band gap is also consistent with the experimental band gap of similar calcite-type structure. A noticeable difference for the LDA and GGA derived transition peaks and a significant optical anisotropy are observed in the optical spectra. The analysis of electronic density of states, Mulliken charge and bonding population shows the coexistence of covalent and ionic bonding in the dolomite structure and the results are consistent with previous theoretical calculations.