Generalized Gradient Approximation Approximation Research Articles

Electronic and Magneto-Electric properties of YFeO3

In this study, we have thoroughly investigated the electronic, magnetic, and electrical properties of yttrium orthoferrite using density functional theory (DFT) within the generalized gradient approximation (GGA) and the (GGA + U) approach, which incorporates the Hubbard term (U). Both approximations consistently reveal a semiconductor behavior and an antiferromagnetic behavior of type-G between the iron (Fe) ions. To delve deeper into the magnetic interactions within YFeO3, we have proposed a physical model. This model allows us to calculate the magnetic exchange coupling and magnetic anisotropy parameters through DFT calculations. Additionally, we have conducted computations to determine the electric polarization. Our results have shown that the electric polarization in YFeO3 is exclusively derived from electronic polarization. We have also explored the relationship between the direction of electric polarization and the easy-axis magnetization. In our investigation, we found that both the electric polarization and easy-axis magnetization align along the c-axis in both approximations. Furthermore, we have examined the influence of the Hubbard term on the direction of polarization. To assess the magnetic temperature transition, we employed Monte Carlo simulations using the Ising model. The critical temperature, denoted as TN, obtained with the GGA approximation is found to be 726.66 K. Remarkably, this value closely matches the experimental critical temperature when compared to the critical temperature obtained with the GGA + U approximation.

Half-metallicity feature within Ag-doped zincblende WGe alloys: DFT+U insights

By employing the full-potential linearized augmented plane wave (FP-L/APW[Formula: see text]lo) technique based on density functional theory (DFT), the structural, electronic and magnetic properties of zincblende W[Formula: see text]AgxGe alloys ([Formula: see text] and 0.25) are scrutinized thoroughly. Based on the generalized gradient approximation (GGA), the exchange-correlation energy functional is included in the current simulation. For computing the structural features, the GGA approximation is applied, whereas GGA, [Formula: see text] and the modified Burke–Johnson of [Formula: see text] (TB-mBJ-[Formula: see text] approximations are incorporated to perform the calculations of electronic and magnetic behaviors of these alloys. The structural analysis of the alloys indicated that the total energy of the W[Formula: see text]Ag[Formula: see text]Ge alloy was favorable in the ferromagnetic ground state. The spin-polarized electronic structure shows the half-metallic behavior of the W[Formula: see text]Ag[Formula: see text]Ge alloy, while the WGe compound is identified as a metal. The magnetic results obtained from the half-metallic W[Formula: see text]Ag[Formula: see text]Ge alloy increasingly support the full half-metallicity of this compound because an integer value is acquired for the total magnetic moment. The strong hybridization between 4p-Ge and 3d-W states brings forth weak local magnetic moments at the nonmagnetic Ge atomic sites and reduces the local magnetic moment of the W atomic sites from its free space charge.

Do Models beyond Hybrid Density Functionals Increase the Agreement with Experiment for Predicted NMR Chemical Shifts or Electric Field Gradient Tensors in Organic Solids?

Ab initio predictions of chemical shifts and electric field gradient (EFG) tensor components are frequently used to help interpret solid-state nuclear magnetic resonance (NMR) experiments. Typically, these predictions employ density functional theory (DFT) with generalized gradient approximation (GGA) functionals, though hybrid functionals have been shown to improve accuracy relative to experiment. Here, the performance of a dozen models beyond the GGA approximation are examined for the prediction of solid-state NMR observables, including meta-GGA, hybrid, and double-hybrid density functionals and second-order Møller-Plesset perturbation theory (MP2). These models are tested on organic molecular crystal data sets containing 169 experimental 13C and 15N chemical shifts and 114 17O and 14N EFG tensor components. To make these calculations affordable, gauge-including projector augmented wave (GIPAW) Perdew-Burke-Ernzerhof (PBE) calculations with periodic boundary conditions are combined with a local intramolecular correction computed at the higher level of theory. Within the context of typical NMR property calculations performed on a static, DFT-optimized crystal structure, the benchmarking finds that the double-hybrid DFT functionals produce errors versus experiment that are no smaller than those of hybrid functionals in the best cases, and they can be larger. MP2 errors versus experiment are even bigger. Overall, no practical advantages are found for using any of the tested double-hybrid functionals or MP2 to predict experimental solid-state NMR chemical shifts and EFG tensor components for routine organic crystals, especially given the higher computational cost of those methods. This finding likely reflects error cancellation benefiting the hybrid functionals. Improving the accuracy of the predicted chemical shifts and EFG tensors relative to experiment would probably require more robust treatments of the crystal structures, their dynamics, and other factors.

Density-functional quantum computations on bandgap engineering and tuning of optoelectronic properties of MgH2 via Mo doping: Prospects and potential for clean energy hydrogen-storage fuel and optoelectronic applications

With the increasing depletion of conventional energy sources and their detrimental environmental hazards, it is imperative to search for sustainable alternative clean energy sources. In the recent decades, hydrogen has emerged as potential source of clean energy. One of the potential alternatives to achieve the objective is the designing and characterization of materials for hydrogen-storage energy applications. In this regard, metal-bearing hydrides are the most promising candidates. For instance, magnesium-bearing hydrides are the focus of current research work owing to high hydrogen capacity of 7.6 wt%. In this paper, we first time report density functional-based quantum theoretical analysis to explore the potential of Mo-doped magnesium hydrides MgH2:Mo for optoelectronic and hydrogen-storage applications. For the quantum computations of the required optoelectronics and energy storage properties, we employed all-electron methods within generalized gradient approximation (GGA). Besides applying GGA approximation to account for the electronic correlated effects, we employed the Hubbard potential U (= 4 eV) for onsite repulsive Coulomb force. We predict that 10% doping by weight of Mo into MgH2 suppresses its insulating band gap of 4.9 eV to semiconducting band gap of order 3.15 eV for spin up and 0.15 eV for spin down. As such the doping of Mo can tune the the bandgap, structural, electronic and optoelectronic properties of MgH2 considerably for potential applications.

Ab-initio study of structural stability, electronic and optical properties of X2GeSe (X = P and Sb) monolayers

This paper investigated the structural stability, electronic and optical properties of X2GeSe (X = P and Sb) monolayers in a hexagonal structure. The calculations are based on the density functional theory using the plane wave method in the Quantum-Espresso computational package for local density approximation (LDA) and the generalized gradient approximation (GGA). The results of phononic calculations indicate that P2GeSe and Sb2GeSe monolayers are dynamically stable in LDA and GGA approximations. The electronic section of X2GeSe (X = P and Sb) monolayers showed that both compounds are semiconductors. The P2GeSe and Sb2GeSe monolayers in the LDA approximation exhibit a direct bandgap at the Γ point with a quantity of 0.88 and 0.84 eV, respectively. Also, P2GeSe and Sb2GeSe monolayers have an indirect bandgap in the GGA approximation in the Г−K path whit amount of 1.07 and 1.02 eV, respectively. For X2GeSe monolayers (X = P and Sb), the optical gaps calculated from the absorption spectrum confirm the electronic bandgap results. The optical calculations showed that the static dielectric constant ε1(0) decreases in the x and z directions but increases in the y-direction with increasing constant atomic radius from P to Sb atom. According to the results, in both LDA and GGA approximations, the maximum reflections of the P2GeSe monolayer are in the ultraviolet domain of the electromagnetic spectrum and for the Sb2GeSe monolayer, the maximum of reflections occurs in the infrared domain. This result makes the studied monolayers a potential candidate for use in optoelectronic devices as a reflector layer of the electromagnetic beam. The calculated of the energy loss spectrum L(ω) diagram shows that the significant collective excitations of the electron charge density in the crystal, which is considered as the plasmonic peak, are in the y-direction. The values of the static refractive index n0, obtained from the squares of the real part of the dielectric function at zero energy, n0=ε1(0), are very close to that of the refractive index diagram at zero energy. For every examined monolayer, the static refractive index in the y-direction is larger than other x and z directions in both LDA and GGA approximations. Examination of the optical properties of the X2GeSe (X = P and Sb) monolayers in different x, y, and z-directions explains the anisotropy of the studied structures.

Structural, electronic, magnetic, optical, thermoelectric and thermodynamic properties of R2Rh3Ge (R=Gd and Er)

The structural, electronic, magnetic, optical, thermoelectric and thermodynamic properties of the Gd2Rh3Ge and Er2Rh3Ge ternary rhombohedral Laves phases compounds were studied by using the density functional theory (DFT) based the full potential linearized augmented plane wave (FPLAPW) with the generalized gradient approximation (GGA). The lattice constants of two compounds are calculated by using the Perdew–Burke–Ernzerhof (PBE)-GGA approximation. The two systems have a metallic character. Density of states as well as magnetic moment confirm that these compounds are ferromagnetic metals. The ferromagnetic state was more stable than paramagnetic state. The dielectric function, reflectivity, energy loss function, absorption coefficient and optical conductivity were calculated. The heat capacities, the thermal expansion coefficient and the Debye temperatures have also been determined from the non-equilibrium Gibbs functions. The negative value of formation energy confirms the stability of these compounds.

Structural, elastic, electronic, thermal, and phononic properties of yttrium carbide: First-principles calculations

In this paper, structural, electronic, elastic, phononic, and thermal properties of YC in both rock-salt (B1) and CsCl (B2) phases are studied. Calculations have been performed by using QUANTUM-ESPRESSO/PWSCF computational package which is based on density functional theory (DFT) and pseudo-potential method. Local density approximation (LDA) and generalized gradient approximation (GGA) have been used for modeling the exchange and correlation effects. According to the total energy diagram versus unit cell volume, the YC compound in the B1 phase is more stable than that of the B2 phase at ambient pressure. The computed elastic parameters indicated that the B2 phase did not satisfy the mechanical stability conditions at ambient pressure and is considered to be an unstable phase of the YC structure.The analysis of the enthalpy versus pressure diagram predicts that the structural phase transition from the B1 phase to the B2 phase occurs at pressures 51 GPa and 71.5 GPa, for various LDA and GGA approximations, respectively. Based on the phonon dispersion curves at ambient pressure, the B1 phase of the YC compound is dynamically stable, while at high pressure, the YC compound in the B2 phase has shown stability. Using calculated elastic constants, the small amount of Zener anisotropy factor A shows a strongly anisotropic nature of the YC structure. The higher amount of the calculated Poisson's ratio (~0.40) than that of the corresponding critical value (~0.33) together with the positive values of Cauchy pressure within the LDA and GGA approximations present the ductility and metallic behavior of the YC compound in the B1 phase. The band structure and total density of states calculations also verify the metallic behavior of the YC compound in the stable B1 phase. From PDOS calculations, overlapping the 4d orbital of the Y atom and 2p orbital of the C atom near the Fermi level indicates that these orbitals have significant contributions to the bonding between the Y and C atoms. This bonding is substantiated by the corresponding electron density distribution. The thermodynamic calculations indicated that the heat capacity increases regularly and continuously with the increase in temperature T, toward the classical Dulong-Petit value of 6R for the bulk structure of the YC compound with two atoms in the primitive cell. It can also be predicted for the YC compound that the smaller lattice parameter within the LDA approximation compared to the GGA approximation causes stiffness increases, followed by an increase in the Debye temperature. The increasing trend of entropy versus temperature indicates the endothermic behavior of the YC compound.

Structural, optical, photoluminescence properties and Ab initio calculations of new Zn2SiO4/ZnO composite for white light emitting diodes

Zn2SiO4/ZnO composite have been prepared via simple solid-state chemical reaction. The obtained sample was investigated by X-ray powder diffraction (XRD) using Full prof program refinement, which confirmed the presence of two phases: the willemite (Zn2SiO4) and the zincite (ZnO). Willemite is a trigonal hexagonal phase with R3‾ space group and the lattice parameters a = b = 13.9387 (Å), c = 9.3088 (Å), α = β = 90° and γ = 120°. Then, the reliability factor was χ2 = 2.02. FTIR and Raman analysis confirmed the formation of both ZnO and Zn2SiO4 by the presence of their characteristic vibration modes. Furthermore, UV–visible measurements showed that the composite exhibited a strong absorbance in UV region, and displayed two gap energies (Eg = 3.02 eV and Eg = 5.5 eV) attributed to ZnO and Zn2SiO4, respectively. Moreover, the composite showed a broadening of visible range emissions compared to both Zn2SiO4 and ZnO. The room temperature photo-luminescence spectrum showed white light emissions at 438 and 533 nm attributed to Zn2SiO4 phase, besides those of ZnO. This makes the new Zn2SiO4/ZnO composite promising to be used in white light emitting diodes. Then, the Ab initio calculations were used to calculate the total and partial density of states as a function of the ZnO and Zn2SiO4 energies. The gap energies calculated using the generalized gradient approximation (GGA) are 0.75 and 3.48 eV for ZnO and Zn2SiO4, respectively. Furthermore, the obtained gap values close to Fermi level (EF) demonstrated the semiconductor character. The Beck-Johnson modified exchange potential approximation (mBJ) is used to improve or to correct the result obtained by GGA approximation. In fact, the obtained gap values matched well with the experimental ones: Ea = 2.87 eV and Ea = 5.53 eV for ZnO and Zn2SiO4, respectively.

Study of structural, and optical properties of the layered perovskite La2Ti2O7 nanoparticle

Nanocrystalline of La2Ti2O7 denoted by LTO is prepared by the sol–gel method in order to investigate their structural and optical properties. X-ray diffraction (XRD) confirmed the complete crystallization of calcined sample at 1050 °C for 3 h. The results display a single-phase as a layered perovskite-type in a monoclinic structure with space group P21. The optical properties were investigated at room temperature by an UV–visible (UV–vis) spectrophotometer. The UV–vis spectrum indicated that the studied powder has an optical bandgap of 3.69 eV. Ab-initio calculations were performed to study the electronic structure using generalized gradient approximation (GGA) and the modified Becke-Jonson (mBJ) to correct the gap energy. The obtained gap energy using GGA is of 2.95 eV, which is far from the value 3.69 eV obtained experimentally and indicating that in this case, GGA approximation underestimates the gap energy. Whereas, the obtained energy using the GGA+mBJ approximation is of 3.64 eV, which is in good agreement to the experimental one.

First-principles investigation of electronic and magnetic properties of some holmium pnictides under pressure

First-principles calculations of the structural, magnetic and elastic properties of Holmium pnictides compounds HoX (X = As, Sb, and P) in the rock-salt structure, as a function of pressure, have been performed using the Density Functional Theory (DFT). We have used two full-potential methods: full potential linearized augmented plane wave (FP-LAPW) implemented in WIEN2k code and full-potential local-orbital minimum-basis in FPLO code. The calculations are carried out within a framework of the generalized gradient approximation (GGA) and GGA+U (where U = 5 eV is the Hubbard correlation term). the total magnetic moments of HoAs, HoSb, and HoP using GGA approximation are 5.85, 6.35, and 5.70 µB respectively and using GGA+U are 5.803, 6.208, 5.634 µB respectively. We investigated the effect of pressure on the magnetic properties of these compounds, using GGA approximation. The total magnetic moment of HoP shows small variation at low pressure, but it decreases rapidly at high pressure to reach 3.87 µB at 50 GPa.

Theoretical study of the structural stability, electronic and magnetic properties of XVSb (X = Fe, Ni, and Co) half-Heusler compounds

The structural, electronic and magnetic properties of half-Heusler compounds XVSb (X $=$ Fe, Co and Ni) are investigated by using the density functional theory with generalized gradient approximation (GGA), and Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potential approximation. It is found that the half-metallic gaps are generally reasonably widened by mBJ as compared to the GGA approximation. The magnetic proprieties of XVSb (X $=$ Fe, Co and Ni) are well defined within mBJ with an exact integer value of magnetic moment. The band gaps given by TB-mBJ are in good agreement with the available theoretical data. The FeVSb exhibits a semiconductor nature. The CoVSb and NiVSb present half-metallic behaviour with total magnetic moment of $1\mu_\text{B}$ and $2\mu_\text{B}$ in good agreement with Slater-Pauling rule. These alloys seem to be a potential candidate of spintronic devices.

Ab initio study of thermodynamic properties of bulk zinc-blende CdS: Comparing the LDA and GGA

In the present study, we have investigated the phonon and thermodynamic properties of bulk zinc-blende CdS by first-principle calculations within the density functional theory (DFT) and the density functional perturbation theory (DFPT) method using the quasi harmonic approximation (QHA). We calculated the phonon dispersion at several high symmetry directions, density of phonon state, temperature dependence feature of Helmholtz free energy (F), internal energy, bulk modulus, constant-volume specific heat, entropy, coefficient of the volume thermal expansion and Grüneisen parameter estimated with the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation potential and compared them with each other. For internal energy, Helmholtz free energy, constant volume heat capacity and phonon entropy the LDA and GGA results are very similar. But, the LDA gives lattice constants that are smaller than GGA while phonon frequencies, bulk modulus and cohesive energies are larger. On the other hand, the results obtained through the GGA approximation for the coefficient of the volume thermal expansion and Grüneisen parameter are larger than those obtained from LDA.

First-principles prediction of insulating antiferromagnet in ordered double-perovskite Ca2MnMoO6 compound

Using first-principle calculations within the framework of density functional theory (DFT), the full-potential linearized augmented plane-wave (FP-LAPW) method have been performed to investigate structural, electronic and magnetic properties of the Ca2MnMoO6 double perovskite. Different spin configurations (ferromagnetic (FM), ferrimagnetic (FiM), and anti-ferromagnetic AFM1, and AFM2) within both generalized gradient approximation (GGA) and [Formula: see text] (Hubbard Coulomb onsite correction) were considered. The value of the Hubbard−Coulomb [Formula: see text] parameter was varied in the range of [Formula: see text][Formula: see text]eV. The ground state is found to be AFM and insulating with the AFM1 state which is the most favorable. In the AFM1 spin configuration, Ca2MnMoO6 compound has a semiconductor nature, with the fully spin-polarized valence and conduction bands in the same spin channel. Within the [Formula: see text] approximation, the FM phase has a half-metallic character with a net magnetic moment of [Formula: see text] while in the anti-ferromagnetic phase it has an insulating character with zero net magnetic moment which was found at [Formula: see text][Formula: see text]eV. We found that in the AFM phase within the GGA approximation, a metallic character is obtained for Ca2MnMoO6 and also for [Formula: see text][Formula: see text]eV. In particular, for Hubbard [Formula: see text] of 3.6[Formula: see text]eV, a small energy gap of 0.20[Formula: see text]eV is observed. The main features shown by the density of states curves motivate further experimental exploration in the double perovskite Ca2MnMoO6 for spintronic applications.

Ab-initio study of structural, elastic, thermal, electronic and magnetic properties of quaternary Heusler alloys CoMnCrZ (Z = Al, As, Si, Ge)

First-principles approach is used to study the structural, electronic and magnetic properties of CoMnCrZ (Z = Al, Si, Ge and As) quaternary Heusler compounds, using full-potential linearized augmented plane wave (FP-LAPW) scheme within the generalized gradient approximation (GGA). The computed equilibrium lattice parameters agree well with the available theoretical data. The obtained negative formation energy shows that CoMnCrZ (Z = Al, Si, Ge, As) compounds have strong structural stability. The elastic constants C ij are calculated using the total energy variation with strain technique. The polycrystalline elastic moduli (namely: the shear modulus, Young’s modulus, Poisson’s ratio, sound velocities, Debye temperature and melting temperature were derived from the obtained single-crystal elastic constants. The ductility mechanism for the studied compounds is discussed via the elastic constants C ij . Our calculations with the GGA approximation predict that CoMnCrGe, CoMnCrAl, CoMnCrSi and CoMnCrAs are half-metallic ferrimagnets (HMFs) with a half-metallic gap E HM of 0.03 eV, 0.19 eV, 0.34 eV and 0.50 eV for, respectively. We also find that the half-metallicity is maintained on a wide range of lattice constants.

Polymorphism of resorcinol explored by complementary vibrational spectroscopy (FT-RS, THz-TDS, INS) and first-principles solid-state computations (plane-wave DFT).

The polymorphism of resorcinol has been complementary studied by combining Raman, time-domain terahertz, and inelastic neutron scattering spectroscopy with modern solid-state density functional theory (DFT) calculations. The spectral differences, emerging from the temperature-induced structural phase transition, have been successfully interpreted with an emphasis on the low-wavenumber range. The given interpretation is based on the plane-wave DFT computations, providing an excellent overall reproduction of both wavenumbers and intensities and revealing the source of the observed spectral differences. The performance of the generalized gradient approximation (GGA) functionals in prediction of the structural parameters and the vibrational spectra of the normal-pressure polymorphs of resorcinol has been extensively examined. The results show that the standard Perdew, Burke, and Ernzerhof (PBE) approach along with its "hard" revised form tends to be superior if compared to the "soft" GGA approximation.

Thermodynamic Properties of Copper in a Wide Range of Pressure and Temperature Within the Quasi-Harmonic Approximation

A first-principles calculations have been performed based on density functional theory to study the thermal properties of copper. Calculations have been performed using the pseudo-potential method within the generalized gradient approximation (GGA) and local density approximation. Thermodynamic properties including the bulk modulus, thermal expansion coefficient, and heat capacities at constant volume and constant pressure were calculated as a function of pressure and temperature using three different models based on the quasi-harmonic approximation: the Debye–Slater model, the Debye–Gruneisen model, and the full quasi-harmonic model (that requires the phonon density of states at each calculated volume). Also, empirical energy corrections are applied to the results of the three models. The electronic contributions to the specific heat are calculated and discussed, and it was found that they become important at high temperatures. The calculated values are in good agreement with experimental results. It is found that the full quasi-harmonic model with the GGA approximation provides more accurate estimates in comparison with the other models.

Electronic structure of lanthanum sesquioxide: A Compton scattering study

We present the first-ever experimental and theoretical momentum densities of La2O3. The Compton line shape is measured using a 20 Ci 137Cs Compton spectrometer at an intermediate resolution with full width at half maximum of 0.34a.u. The experimental Compton profile is compared with the theoretical electron momentum densities computed using linear combination of atomic orbitals (LCAO) method with density functional theory (DFT). It is seen that the generalized gradient approximation (GGA) within DFT reconciles better with the experiment than other DFT based approximations, validating the GGA approximation for rare-earth sesquioxides. The energy bands and density of states computed using LCAO calculations show its wide band gap nature which is in tune with the available reflectivity and photo-absorption data. In addition, Mulliken׳s population and charge density are also computed and discussed.

Structural, Elastic, and Electronic Properties of CuClxBr(1-x) Compounds under Pressure

We have applied the pseudo-potential plane wave (PP-PW) method to study the structural, elastic, and electronic properties of CuClxBr(1-x) under high pressure using the generalized gradient approximation (GGA). The effect of Cl substitutional impurities (x) on the lattice parameters for both the GGA and virtual crystal approximation (VCA) approaches were studied. The pressures at which the compounds CuClxBr(1-x) undergo a structural phase transition from ZnS type to NaCl type Pt were calculated. The elastic constants at various pressures in the 0 ＜ x ＜ 1 composition range were presented. The longitudinal-wave mode speed (VL) and transverse-wave mode speed (VT) in CuClxBr(1-x) propagating in the [100], [110], and [111] directions at zero pressure for various Cl compositions (x) in the range 0-1 were investigated. The band structure and band gap-pressure coefficients are also given. The calculated effective masses of electrons and heavy and light holes in the material under study for different concentrations x are presented.

First-principles study of electronic structure and elasticity of UAlx (x=1,2,3) system

Abstract A detailed theoretical study of structural, electronic, and elastic properties of cubic UAlx (x=1,2,3) is presented employing the pseudopotential plane-wave method based on density-functional theory. The structure parameters of these three compounds have been calculated within generalized gradient approximation (GGA) and local density approximation (LDA). The calculated results were compared with the experimental data and previous research. With the GGA approximation, the elastic constants, shear modulus, Young's modulus, and Poisson's ratio of UAlx (x=1,2,3) are derived. According to the generalized mechanical stability criteria for cubic crystals, our calculation suggested that C15 UAl2 and L12 UAl3 are stable substance under hydrostatic pressures, but B2 UAl might be expected as a metastable compound, which is not reported in previous literature, and future experimental confirmation is needed. Furthermore, the calculated energy band structure and density of state (DOS) are found to be in good agreement with the theoretical values. Additionally, the charge density of these compounds have also been worked out and analyzed.

Theoretical study on electronic properties and pressure-induced phase transition in β-CdP 2

In this paper, both the local density approximation (LDA) and the generalized gradient approximation (GGA) are used to investigate the structural and electronic properties of the β modification of CdP 2 ( β-CdP 2) at zero pressure. In addition, the energy band structure, electron density of states (DOS) and projected density of states (PDOS) analysis of β-CdP 2 are presented. What is more, we study the properties of β-CdP 2 in the pressure range of 0–20 GPa, show the variations of the cell volume and band gap with the pressure for both LDA and GGA approximation. Then, the bulk modulus B 0 and its first pressure derivative B 0 ′ obtained by fitting different equations of state (EOS) to the pressure–volume ( P– V) relation at ambient pressure are presented and compared with the available experimental data. At the end of our study, we for the first time find that a pressure-induced structural phase transition from the tetragonal phase ( β-CdP 2) to a orthorhombic phase (α-CdP 2) when the pressure is increased to a value between 20 and 25 Gpa in theory.