Plane-wave Pseudopotential Density Functional Theory Research Articles

The structures, phase transition and elastic and thermodynamic properties of ZnS from first-principles calculations

The phase transition of zinc sulfide (ZnS) from Zinc-blende (ZB) to a rocksalt (RS) structure and the elastic, thermodynamic properties of the two structures under high temperature and pressure are investigated by first-principles study based on the pseudo-potential plane-wave density functional theory (DFT) combined with the quasi-harmonic Debye model. The lattice constant [Formula: see text], bulk modulus [Formula: see text] and the pressure derivative of bulk modulus [Formula: see text]’ of the two structures are calculated. The results are in good agreement with experimental results and the other theoretical data. From the energy–volume curve, enthalpy equal principle and mechanical stability criterion, the transition pressures from the ZB to the RS structure are 16.83, 16.96 and 16.61 GPa, respectively. The three results and the experimental values 14.7–18.1, 16 GPa are very close to each other. Then the elastic properties are also calculated under the pressure ranging from 0 to 30 GPa. Finally, through the quasi-harmonic Debye model, the thermodynamic properties dependence of temperature and pressure in the ranges between 0–1600 K and 0–30 GPa are obtained successfully.

Ab initio study of structural, electronic and thermodynamic properties of Be12V under high temperature

The structure, electronic, elasticity and thermodynamic properties, phonon spectra of Be12V alloy under high temperatures and pressure are investigated by using first-principles calculations based on pseudo-potential plane-wave density functional theory method within using the generalized gradient approximation (GGA) and quasi-harmonic Debye model. The results show that the calculated equilibrium structural parameters of Be12V are in good agreement with the experiments. Under high pressure, the elastic constant of Be12V alloy increases with the increase of pressure. The all elastic constants satisfy the Born's mechanical criterion, indicating that Be12V crystal is dynamic stable under the applied pressure (0 GPã50 GPa), and the pressure has little effect on the electronic properties of Be12V. The phonon spectra and phonon density of states under pressure from 0 GPa to 50 GPa are presented for the Be12V and discussed the effects of pressure on some properties. By the quasi-harmonic Debye model, the thermodynamic properties of Be12V under high temperature and pressure were predicted, and the relationship of heat capacity, thermal expansion coefficient with temperature and pressure was obtained in the range of 0–1300 K and 0–20 GPa, respectively.

Structural stability, mechanical, electronic and thermal behaviour of Ru2CrZ (Z=Sb, Si, Pb, Ge) Heusler alloys

In this paper, the structural, elastic, electronic properties of Ru2CrZ (Z=Si, Ge, Pb, Sn) are explored using the generalized gradient approximation based on ab initio plane-wave pseudopotential density functional theory. With the help of the quasi-harmonic Debye model, we also investigate the variation of normalized volume V/V0, the heat capacities CV and CP, thermal expansivity, and Debye temperature of Ru2CrZ (Z=Si, Ge, Pb, Sn). Results show that the Cu2MnAl type structure is more stable then Hg2CuTi type structure. The four compounds in the ground state are predicted to be nearly half-metal behavior with total magnetic moment near to the integer value. To provide a comparative and complementary study to future researches, we investigated the elastic and thermodynamic properties.

First Principles Calculations on Elastic, Thermodynamic and Electronic Properties of Co2Zr and Co2Ti at High Temperature and Pressure

Co2Zr and Co2Ti are both cubic crystals with a Cu2Mg-type structure. The elastic, thermodynamic and electronic properties of the intermetallic compounds Co2Zr and Co2Ti are investigated by using ab initio plane-wave pseudopotential density functional theory (PWPDFT) and generalized gradient approximation (GGA) under high temperature and pressure. The partially calculated results are consistent with the available experimental data. The elastic properties of Co2Zr and Co2Ti under high pressure were first studied by first principles calculations. The results indicate that the elastic constants, elastic modulus and Poisson’s ratio are functions of pressure, indicating that the effect of pressure on the ductility and anisotropy is significant. The thermodynamic properties are also calculated by the quasi-harmonic Debye model. In the range of 0~100 GPa pressure and 0~1500 K temperature, the Debye temperature Θ, the heat capacity CV and the thermal expansion α vary with pressure and temperature. Co2Ti has a higher Debye temperature than Co2Zr under the same pressure. Decreasing temperature and increasing pressure have the same effects on CV and α. The electron density difference and density of states of Co2Zr and Co2Ti are finally investigated. The results show that both Co2Zr and Co2Ti are typically metal crystals but Co2Zr has greater covalence than Co2Ti.

The structural and elastic properties of a full-Heusler compound Cu2MnAl under pressure

First-principles calculations of the crystal structure and the elastic constants of Cu2MnAl Heusler compound have been investigated by the plane-wave pseudopotential density functional theory method. The calculated lattice and elastic constants are in agreement with the experimental and existing theoretical calculations. Based on the elastic constants, the aggregate elastic moduli (B, G), Poisson�s ratio, elastic anisotropy, melting point and Debye temperature with pressure have been investigated. It is found that the ductility, elastic anisotropy, melting point and Debye temperature increase with increasing pressure.

First-principles investigations of crystal structures and physical properties of jadeite under various pressures

The crystal structures, electronic, elastic properties, hardness and phase transition of jadeite under various pressures from 0 to 70 GPa are investigated by using the first-principles calculations based on plane-wave pseudopotential density functional theory within the generalized gradient approximation (GGA). The calculated lattice parameters a, b and c were found perfectly agree with the available experimental data below 10 GPa. They all present linear responses to pressure until 60 GPa, lattice parameters present nonlinear variations. The calculation results show compression along a-axis is more difficult than that along b-axis or c-axis which can be explained by the alternative arrangement of SiO tetrahedron and AlO octahedron along a-axis. The elastic constants, bulk modulus, shear modulus, Young's modulus, B/G, Poisson's ratio, hardness and electronic properties are further investigated as a function of pressure which all present anomaly at 60 GPa. The generalized Born's mechanical stability criterion present jadeite is mechanical unstable above 62 GPa. The calculation results all present phase transition of jadeite occurs above 60 GPa, which agree with the available experimental data and other theoretical results.

Effect of tellurium concentration on the structural, electronic and mechanical properties of beryllium sulphide: A DFT approach

The structural, electronic and mechanical properties of are studied within the concentration range of using first-principles plane–wave Pseudopotential density functional theory (DFT) approach. We have used generalized gradient approximation (GGA) to treat the exchange-correlation potentials. The elastic constants, bulk, shear and Young’s moduli, Poisson’s ratio, and Zener’s anisotropic factors are calculated. The results were found to be in agreement with other available theoretical and experimental values. It was also observed that the existence and increase of Tellurium concentration decreases the hardness of the alloy.

Newly synthesized MgAl2Ge2: A first-principles comparison with its silicide and carbide counterparts

Using plane-wave pseudopotential density functional theory (DFT), the first-principle calculations are performed to investigate the structural aspects, mechanical behaviors and electronic features of the newly synthesized CaAl2Si2-prototype intermetallic compound, MgAl2Ge2 for the first time and the results are compared with those calculated for its silicide and carbide counterparts MgAl2Si2 and MgAl2C2. The calculated lattice constants agree fairly well with their corresponding experimental values. The estimated elastic tensors satisfy the mechanical stability conditions for MgAl2Ge2 along with MgAl2Si2 and MgAl2C2. The level of elastic anisotropy increases following the sequence of X-elements Ge → Si → C. MgAl2Ge2 and MgAl2Si2 are expected to be ductile and damage tolerant, while MgAl2C2 is a brittle one. MgAl2Ge2 and MgAl2Si2 should exhibit better thermal shock resistance and low thermal conductivity and accordingly these can be used as thermal barrier coating (TBC) materials. The Debye temperature of MgAl2Ge2 is lowest among three intermetallic compounds. MgAl2Ge2 and MgAl2Si2 should exhibit metallic conductivity; while the dual characters of weak-metals and semiconductors are expected for MgAl2C2. The values of theoretical Vickers hardness for MgAl2Ge2, MgAl2Si2, and MgAl2C2 are 3.3, 2.7, and 7.7 GPa, respectively, indicating that these three intermetallics are soft and easily machinable.

High-pressure and high-temperature physical properties of LiF studied by density functional theory calculations and molecular dynamics simulations

Using the revised Perdew-Burke-Ernzerhof generalized gradient approximation based on first-principles plane-wave pseudopotential density functional theory, the high-pressure structural phase transition of LiF is explored. From the analysis of Gibbs free energies, we find that no phase transition occurs for LiF in the presented pressure range from 0 to 1000 GPa, and this result is consistent with the theoretical prediction obtained via ab initio calculations [N.A. Smirnov, Phys. Rev. B 83 (2011) 014109]. Using the classical molecular dynamics technique with effective pair potentials which consist of the Coulomb, dispersion, and repulsion interaction, the melting phase diagram of LiF is determined. The obtained normalized volumes under pressure are in good agreement with our density functional theory results and the available experimental data. Meanwhile, with the help of the quasi-harmonic Debye model in which the phononic effects are considered, the thermodynamic properties of interest, including the volume thermal expansion coefficient, isothermal bulk modulus and its first and second pressure derivatives, heat capacity at constant volume, entropy, Debye temperature, and Grüneisen parameter of LiF are predicted systematically. All the properties of LiF with the stable NaCl-type structure in the temperature range of 0–4900 K and the pressure up to 1000 GPa are summarized.

Pressure-induced improvement in symmetry and change in electronic properties of SnSe.

To explore the structural and electronic properties of SnSe under pressure, we applied hydrostatic pressure from 0 to 8GPa to a fully relaxed SnSe cell sample based on plane-wave pseudopotential density functional theory. The calculated results indicate that the structure of SnSe changes gradually from an irregular zigzag structure with low symmetry to a B1-like structure with regular arrangement and high symmetry under pressure. The lattice parameters and cell volume of SnSe decrease monotonically as the applied pressure increases. The energy band gap of SnSe becomes narrow under pressure and is finally closed at 6.1GPa. Moreover, we found that SnSe exhibits non-magnetic and semi-metallic features based on analyzing its electronic state density and spin state density. This can be attributed to the decrease in the lattices constants and the enhancement of the Sn-Se bond interaction under pressure, which causes the density of electronic states to increase near the Fermi surface. Finally, the charge distribution between Se-Sn-Se along the c-axis changes gradually from asymmetric to symmetric as the pressure is increased to 6.1GPa and beyond. This implies that enhancement of the structure symmetry of SnSe can lead to a symmetrical distribution of charges, which further affects the bonding characteristics of the Sn-Se bond.

Phase transition and high-pressure thermodynamic properties of CdN derived from first-principles and quasi-harmonic Debye model

The structural phase transition and thermodynamic properties of CdN under high pressure and temperature are investigated by first-principles calculations based on the plane-wave pseudopotential density functional theory method combined with the quasi-harmonic Debye model. It can be found that the rocksalt phase of CdN is more stable than the zincblende phase in the pressure range of 0–100 GPa based on the enthalpy versus pressure relations. The variations of the volume, thermal expansion, specific heat, entropy, and Debye temperature with pressure and temperature of CdN in rocksalt structure are obtained systematically for the first time.

Effect of different RE site ionic radii on the electronic structures and elastic properties of Ba2RENbO6: A first-principles study

RE site ionic radius has a critical influence on the properties of double perovskite oxide Ba2RENbO6. In this paper, the electronic structures and elastic properties of Ba2RENbO6 (RE = Ho, Er, Yb) have been calculated by using the plane-wave pseudopotential density functional theory, and the effect of the different RE site ions on the structures and properties of Ba2RENbO6 is discussed. Results indicate that Ba2RENbO6 (RE = Ho, Er, Yb) are all direct bandgap semiconductors with a bandgap of 0.95 eV, 1.26 eV and 2.36 eV, respectively. With the decrease of the RE site ionic radius of Ba2RENbO6 (RE = Ho, Er, Yb), RE–O and Nb–O covalent bonds are enhanced, and the elastic constants ([Formula: see text], [Formula: see text], [Formula: see text]), elastic modulus ([Formula: see text], [Formula: see text], [Formula: see text]), [Formula: see text], Poisson’s ratio ([Formula: see text]), the Debye temperature [Formula: see text], Gruneisen parameters [Formula: see text] all show a trend of increase. The elastic and thermodynamic properties are all improved with the decreasing radius of RE site ion.

Investigations of press-induced band gap changes in PbS

We applied the hydrostatic and uniaxial pressure respectively to cubic PbS based on the plane-wave pseudo-potential density functional theory. The calculated results indicate that the band gap of PbS closes and reopens under hydrostatic pressure like a topological crystalline insulator, although it isn't a topological crystalline insulator because the pressure induced phase transition will occur when the hydrostatic pressure increases to about 2.2GPa in fact. In addition, we find that, unlike the case of hydrostatic pressing, when the uniaxial pressure is applied along [001] direction, PbS is converted from a direct band gap semiconductor to an indirect band gap semiconductors.

Investigation of structural, electronic and optical properties of hexagonal LuFeO3 using first principles LDA + U

Extensive research of a new multiferroic material has been conducted due to its possibility of existing in more than one ferroic order—for example ferroelectricity, (anti-)ferromagnetism and ferroelasticity—which gives additional functionalities to a material. In this work, the structural, electronic and optical properties of LuFeO3 in the antiferromagnetic (AFM) hexagonal P63cm phase have been investigated using first-principles calculations based on the local density approximation with Hubbard U (LDA + U) method in the frame of plane-wave pseudopotential density functional theory (DFT). The LDA + U method is implemented to improve the accuracy of the calculated properties of materials which contain strong electronic localized d/f orbitals. The Coulomb repulsion U of 3 eV was chosen. The G-type AFM arrangement of hexagonal LuFeO3 is reported to stabilize more than another type of spin AFM and ferromagnetic arrangement. The direct band gap of 0.54 eV is calculated from the band structure. Other than that, the dielectric constant is shown to be 4.6. The theoretical data from this work could be used as a reference for experimental works and provides important information for future applications.

First-principles calculations for transition phase, mechanical and thermodynamic properties of ZnS under extreme condition

The structural and mechanical properties of ZnS in both B3 and B1 phases have been investigated by the generalized gradient approximation (GGA) within the plane-wave pseudopotential density functional theory (DFT). The obtained lattice parameters and bulk modulus of ZnS for both B3 and B1 structures are well in line with the available theoretical and experimental results. Using the enthalpy–pressure data, we have predicted that the phase transition pressure of ZnS from B3 to B1 is 17.26 GPa, which is in good agreement with previous experimental values. The hydrostatic pressure-dependent elastic properties of the two structures, such as bulk modulus, shear modulus and Young’s modulus, are discussed. Then, the mechanical characteristics of ZnS, including ductile/brittle behavior and elastic anisotropy of the two cubic single-crystal structures, are investigated in details. Furthermore, the thermodynamic properties of ZnS under extreme condition are explored by quasi-harmonic Debye modeling. The calculated results show that the ductility and elastic anisotropy increase with pressure clearly except the ductility of B1. Besides, the temperature and pressure dependencies of the heat capacity and the Debye temperature are obtained and analyzed in the wide ranges.

Anisotropic elastic properties of FexB (x = 1, 2, 3) under pressure. First-principles study

AbstractSpin-polarization (SP) and pressure effects have been used to better clarify and understand anisotropic elastic properties of Fe-B intermetallic compounds using the first-principles calculation with generalized gradient approximation (GGA) within the plane-wave pseudopotential density functional theory. Elastic properties, including bulk, shear and Young’s moduli as well as Poisson ratio were obtained by Voigt-Reuss-Hill approximation. All studied Fe-B compounds were mechanically stable. The brittle and ductile properties were discussed using bulk to shear moduli ratio (B/G) of the studied structures in the pressure range of 0 GPa to 90 GPa in order to predict the critical pressure of phase transition from ferromagnetic (FM) to nonmagnetic (NM) state. Mechanical anisotropy in both cases was discussed by calculating different anisotropic indexes and factors. We have plotted three-dimensional (3D) surfaces and planar contours of the bulk and Young’s moduli of FexB (x = 1, 2, 3) compounds for some crystallographic planes, (1 0 0), (0 1 0) and (0 0 1), to reveal their elastic anisotropy. On the basis of anisotropic elastic properties the easy and hard axes of magnetization for the three studied compounds were predicted.

Density functional study of the high-pressure behavior of Ta3N5

In this paper, the effects of high pressure on the structural, elastic and electronic properties of new synthesized U3Te5-type and U3Se5-type Ta3N5 are investigated by plane-wave pseudopotential density functional theory. The cell volumes, lattice constants and elastic constants of U3Te5-type and U3Se5-type Ta3N5 under pressure ranging from 0 to 100GPa are obtained. The Vickers hardness and Debye temperature of U3Te5-and U3Se5-type Ta3N5 are calculated for the first time. DOS and PDOS are calculated to study the electronic properties and covalent bonds between N and Ta atoms, which are considered to be the origin of the high hardness of these two types Ta3N5.

First-principles investigations on structure and thermodynamic properties of CaS under high pressures

First-principles calculations of the electronic structure and thermodynamic properties of calcium sulfide (CaS) have been carried out by the plane-wave pseudopotential density functional theory method. The calculated values of lattice constant, elastic modulus and its derivative for CaS under zero pressure and zero temperature, agree well with the experimental data and some of the existing model calculations. The band structure and density of states are discussed in detail. Moreover, the dependences of the volume variation, bulk elastic modulus, thermal expansion coefficient and heat capacity on pressure have been investigated for the first time, so far as we know. It is concluded that under the condition of zero temperature (0 K) and zero pressure (0 GPa), the volume is 44.6 3 when the energy of the crystal unit cell reaches a minimum in the structural model of CaS, which is the most stable system. The energy band of CaS is mainly composed of low band gap, valence band and conduction band, the GV-XC band gap of CaS is 2.435 eV. The DOS results show that the valence band is mainly of Ca 3s and S 3p, while the conduction band is mainly of Ca 4d and a small amount of S 3p. At a certain temperature, the volume change rate, heat capacity and thermal expansion coefficient decrease with rising pressure, and the body elastic modulus B increases simultaneously. In contrast, when the pressure is constant, the volume change rate and body elastic modulus B decrease with the increase of temperature, while the thermal expansion coefficient and heat capacity increase as the temperature rises. When the temperature is higher than a certain value, the heat capacity CV is close to the Dulong-Petit limit, and the effect of temperature on the heat capacity is minimal. Furthermore, under the condition of low pressures, the influence of temperature on thermal expansion coefficient is greater than that of the pressure on it.

Self-interaction corrected LDA + U investigations of BiFeO3 properties: plane-wave pseudopotential method

The structural, electronic, elastic, and optical properties of BiFeO3 were investigated using the first-principles calculation based on the local density approximation plus U (LDA + U) method in the frame of plane-wave pseudopotential density functional theory. The application of self-interaction corrected LDA + U method improved the accuracy of the calculated properties. Results of structural, electronic, elastic, and optical properties of BiFeO3, calculated using the LDA + U method were in good agreement with other calculation and experimental data; the optimized choice of on-site Coulomb repulsion U was 3 eV for the treatment of strong electronic localized Fe 3d electrons. Based on the calculated band structure and density of states, the on-site Coulomb repulsion U had a significant effect on the hybridized O 2p and Fe 3d states at the valence and the conduction band. Moreover, the elastic stiffness tensor, the longitudinal and shear wave velocities, bulk modulus, Poisson’s ratio, and the Debye temperature were calculated for U = 0, 3, and 6 eV. The elastic stiffness tensor, bulk modulus, sound velocities, and Debye temperature of BiFeO3 consistently decreased with the increase of the U value.

Ab Initio Calculation of Structure and Thermodynamic Properties of Zintl Aluminide SrAl2

Abstract The structural and thermodynamic properties of the orthorhombic and cubic structure SrAl2 at pressure and temperature are investigated by using the ab initio plane-wave pseudopotential density functional theory methodwithin the generalised gradient approximation (GGA). The calculated lattice parameters are in agreement with the available experimental data and other theoretical results. The phase transition predicted takes place at 0.5 GPa from the orthorhombic to the cubic structure at zero temperature. The thermodynamic properties of the zinc-blende structure SrAl2 are calculated by the quasi-harmonic Debye model. The pressure–volume relationship and the variations inthe thermal expansion α are obtained systematically in the pressure and temperature ranges of 0–5 GPa and 0–500 K, respectively.