First principle investigation of the structural,electronic and elastic properties of the Laves phase compounds SrX2 (X = Pd and Pt)

Structural, electronic and elastic properties of the cubic Laves phases SrX₂ (X = Pd and Pt) with Fd-3 m (No. 227) space group and crystallize in the MgCu₂ structure are studied using the all-electrons full potential linearized augmented plane wave (FP-LAPW) method as implemented in the Wien2k code. The exchange-correlation potential (E_xc) was treated within the scheme of Perdew, Burke, and Ernzerhof generalized gradient approximation (PBE-GGA). In present calculations, studied compounds show a metallic characteristic. When the palladium element was replaced with the platinum, the Fermi level was observed to be increased, indicating an increase in the additional valence electrons that filled the hybridized bonding states. The elastic constants were calculated for both compounds and show that the two compounds suitably verify the Born's mechanical stability criteria and have the ductile manner behaviors.     

Investigation of structural,half-metallic and elastic properties of a new full-Heusler compound–Ir2MnSi

The electronic structure, magnetic and elastic properties of Ir₂MnSi full-Heusler compound is studied within the framework of Density Functional Theory (DFT). The ferromagnetic (FM) and non-magnetic (NM) states are compared in Cu₂MnAl and Hg₂CuTi prototype structures. The ferromagnetic state in Cu₂MnAl structure has been found energetically more stable than non-magnetic state in these two types of structures. Due to this stability, all calculations are carried out for FM-state. The spin-polarized calculations show that the spin-up electrons of Ir₂MnSi compound have metallic nature, but the spin-down electrons have semiconducting behavior with 0.55 eV energy gap around the Fermi level. The calculated Cauchy pressure and Poisson's ratio indicated that Ir₂MnSi compound is a ductile material. Ir₂MnSi compound is a half-metallic ferromagnet (HMF) and it has 5µ_B magnetic moment. This study will theoretically lead to experimental works in the spintronic field and its applications.     

An examination of the structural,electronic, elastic,vibrational and thermodynamic properties of Ru2YGa (Y = Sc,Ti and V) Heusler alloys

The structural, electronic, elastic, vibrational and thermodynamic properties of the Ru₂YGa (Y = Sc, Ti and V) Heusler alloys in L2₁ type cubic structure have been analyzed systematically using first principles density functional theory (DFT) together with the Generalized Gradient Approximation (GGA) method. The values of calculated lattice constant (a₀), elastic constants (Cij), Bulk modulus (B), Shear modulus (G), ratios of B/G, Young's modulus (E) and Poisson ratio (ν) are in good agreement with the available theoretical and experimental results. The electronic band structures, corresponding total and partial density of states have also been obtained. The calculated band structures demonstrate that Ru2YGa (Y = Sc, Ti and V) alloys are metallic. The phonon dispersion curves, total and partial density of states of these alloys have been computed for the first time by adopting the direct method. It is considered that all alloys are dynamically stable in L2₁ structure.     

Insight into the structural,elastic, electronic,thermoelectric, thermodynamic and optical properties of MRhSb (M = Ti,Zr, Hf) half-Heuslers from ab initio calculations

A detailed theoretical investigation on the structural, elastic, electronic, thermoelectric, thermodynamic and optical properties of half-Heusler MRhSb (M = Ti, Zr, Hf) compounds is presented. The computations are carried out using the full potential linear augmented plane wave method (FP-LAPW) within density functional theory (DFT). The optimized lattice parameters are in fairly good agreement with available experimental data. The computed elastic constants (C_ij) and their related elastic moduli confirm the stability of the studied compounds in the cubic phase and highlight their ductile nature. Analysis of band structures and densities of states (DOS) profiles reveal the semiconducting nature with an indirect energy band gap (Γ-X). The bonding nature discussed via the electron charge density plot shows a mixture of covalent and ionic character. The evaluation of Seebeck coefficient leads to thermopower S ≥ 500 µeV which is very benefic for thermoelectric applications. Estimated thermodynamic characteristic within the quasi-harmonic approximation shows similar behavior for the three compounds. Finally, some optical spectra such as the complex dielectric function, refractive index, reflectivity, energy loss function and absorption are presented.     

DFT study of structural,electronic and elastic properties of two polymorphs of monoclinic CsGaQ2 (Q = S,Se)

In this paper, we report an ab-initio calculations of the structural, electronic and elastic properties of monoclinic CsGaQ₂ (Q?=?S, Se) crystals in two polymorphs CsGaQ₂-mC64 and CsGaQ₂-mC16 (Q?=?S, Se). The investigation is done using the pseudo-potential plane-wave (PP-PW) method combined to the generalized gradient approximation (GGA) within the density functional theory (DFT). The calculated equilibrium lattice constants (a, b and c), angle β are in good agreement with the available experimental data. We have calculated and analyzed the energy gap, band structure and density of states. The electronic structure calculation demonstrates that crystals are direct-gap semiconductors. The single-crystal elastic constants C_ij of CsGaQ₂-mC16 are predicted, for the first time, using the stress–strain method. The polycrystalline bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio?ν, and elastic anisotropy A^U are determined based on the predicted C_ij. Our results indicate that CsGaQ₂ (Q?=?S, Se) can be classified as brittle materials.     

The structural,electronic and magnetic properties of Ag4M and Ag4MCO (M = Sc–Zn) clusters

The structures, spectra and electronic and magnetic properties of Ag₄M and Ag₄MCO (M?=?Sc–Zn) clusters have been studied using density functional theory and CALYPSO structure searching method. Structural searches show that M atoms except Zn tend to occupy the highest coordination position in the ground state Ag₄M and Ag₄MCO clusters. Carbon monoxide is most easily adsorbed on Ag atom of Ag₄Zn and M atom of other Ag₄M. Infrared and Raman spectra, photoabsorption spectra and photoelectron spectra of Ag₄M and Ag₄MCO clusters are forecasted and can be used to identify these clusters from experiment. Analysis of electronic properties indicates that the adsorption of CO on Ag₄M clusters changes the zero vibrational energy (ZPVE) and increases stability of the host clusters. Dopant atoms except for Zn improve the stability of silver cluster. The Ag₄Ni cluster shows high chemical activity and maximum adsorption energy for carbon monoxide. Magnetism calculations reveal that the magnetic moment of Ag₄M (M?=?Mn–Ni) cluster adsorbed by carbon monoxide is decreased by 2 μ_B. The change of magnetic moment makes it possible to be used as a nanomaterial for carbon monoxide detection. Simultaneously, it is found that the adsorption of CO on Ag₄Cu cluster is a physical adsorption.     

First principles prediction of the elastic,electronic and optical properties of Sn3X4 (X = P,As, Sb,Bi) compounds: Potential photovoltaic absorbers

We report a first-principles study of structural, mechanical and optoelectronic properties of the Sn₃X₄ (X = P, As, Sb, Bi) compounds. The calculations were performed using the full-potential linearized augmented plane wave approach (FP-LAPW). The structural and mechanical properties of Sn₃X₄ (X = P, As, Sb, Bi) compounds were obtained using GGA-PBE. In addition, The Tran-Blaha modified Becke-Johnson exchange potential (TB-mBJGGA) technique was used to calculated the optoelectronic properties. The calculated electronic band structures and density of states reveal a direct band gap at Γ points varied from 0.11 eV to 1.23 eV for X = P, As, Sb, Bi. The optical absorption calculations show that all compounds have high absorption coefficients about twenty times greater than that of CuInSe₂ and CdTe in the visible region. The high absorption of these materials could be attributed to the localized p-states of cation (X = P, As, Sb, Bi) in the lower region of the conduction band.     

Mechanic,electronic and optical properties of silicides MSi (M = Re,Tc): First-principle calculations

As transition metal silicides have been successfully synthesized, the study of the combination of transition metal and silicon is another effective way to investigate the properties of silicide. We recover novel structures of two silicides: MSi (M?=?Tc, Re). The structures phase are $??FeSi$ phase (P213) and CsCl phase (Pm3m). Using the Cambridge Serial Total Energy Package (CASTEP) code, we researched the mechanical, electronic and optical properties of MSi (M?=?Tc, Re) under 0?GPa and 100?GPa. It is found that each structure is dynamically and mechanically stable at 0?GPa, and the Vickers hardness values show that all of them belong to soft materials. Besides, both the P213-MSi and Pm3m-MSi have metallic characters under 0?GPa and 100?GPa. For the reflectivity in the optical properties, it can be observed that the atom and pressure have obvious influence on the reflectivity of Pm3m-MSi, while only the pressure has obvious influence on the reflectivity of P213-MSi. We hope our work will provide some help to the experimental work on the technologically material.     

Crystal structure and magnetic properties of pseudoternary TbRh2−xMxSi2(M = Ru,Ir) compounds

The structural and magnetic characteristics of the pseudoternary TbRh_2−xM_xSi₂(M = Ru, Ir) compounds were studied. The compounds crystallize in the tetragonal ThCr₂Si₂-type structure. The magnetic data were collected in the temperature range 70–300 K. Their magnetic susceptibilities satisfy the Curie-Weiss law in the temperatures higher than 130 K. The magnetic moment of the rare earth atom is larger than of the free Tb³⁺ ion. A modified RKKY theory with included interaction between the conduction electrons was applied to explain the variation of properties of the compounds.     

Probing the structural,electronic and magnetic properties of small Au4M (M = Sc–Zn) clusters

Density-functional method PW91 has been selected to investigate the structural, electronic and magnetic properties of Au₄M (M =Sc–Zn) clusters. Geometry optimisations show that the M atoms in the ground-state Au₄M clusters favour the most highly coordinated position. The ground-state Au₄M clusters possess a solid structure for M = Sc and Ti and a planar structure for M = V–Zn. The characteristic frequency of the doped clusters is much greater than that of pure gold cluster. The relative stability and chemical activity are analysed by means of the averaged binding energy and highest occupied molecular orbital and lowest unoccupied molecular orbital energy gap for the lowest energy Au₄M clusters. It is found that the dopant atoms can enhance the thermal stability of the host cluster except for Zn atom. The Au₄Ti, Au₄Mn and Au₄Zn clusters have relatively higher chemical stability. The vertical detachment energy, electron affinity and photoelectron spectrum are calculated and simulated theoretically for all the ground-state structures. The magnetism calculations reveal that the total magnetic moment of Au₄M cluster is mainly localised on the M atom and vary from 0 to 5 μ_B by substituting an Au atom in Au₅ cluster with different transition-metal atoms.     

The structural,elastic, and electronic properties of ZrxNbl-xC alloys from first principle calculations＊

The structural, elastic, electronic, and thermodynamic properties of ZrxNbl xC alloys are investigated using the first principles method based on the density functional theory. The results show that the structural properties of Zr~.Nb1 xC alloys vary continuously with the increase of Zr composition. The alloy possesses both the highest shear modulus （215 GPa） and a higher bulk modulus （294 GPa）, with a Zr composition of 0.21. Meanwhile, the Zr0.2! Nb0.79C alloy shows metallic conductivity based on the analysis of the density of states. In addition, the thermodynamic stability of the designed alloys is estimated using the calculated enthalpy of mixing.     

First-principles calculation of the structural,electronic, elastic,and optical properties of sulfur-doping ε-GaSe crystal

The structural,electronic,mechanical properties,and frequency-dependent refractive indexes of GaSe_(1-x)S_x(x=0,0.25,and 1) are studied by using the first-principles pseudopotential method within density functional theory.The calculated results demonstrate the relationships between intralayer structure and elastic modulus in GaSe_(1-x)S_x(x=0,0.25,and 1).Doping of ε-GaSe with S strengthens the Ga-X bonds and increases its elastic moduli of C_(11) and C_(66).Born effective charge analysis provides an explanation for the modification of cleavage properties about the doping of e-GaSe with S.The calculated results of band gaps suggest that the distance between intralayer atom and substitution of S_(Se),rather than interlayer force,is a key factor influencing the electronic exciton energy of the layer semiconductor.The calculated refractive indexes indicate that the doping of ε-GaSe with S reduces its refractive index and increases its birefringence.     

Superalkali NM4 (M = Li,Na, K): Stabilities and electronic structures

Superatoms are clusters that mimic the chemistry of atoms and new materials with unique properties can be synthesized from them. Superalkali NM₄ clusters with homo- and hetero-alkalis M = Li, Na, K are designed, and their vertical ionization potentials (3.22 ～ 3.74 eV) are lower than that of Cs atom. The stabilities of the superalkalis are guaranteed by the binding energies and positive energies of the dissociation channel NM₃ + M, and NLi₄ is the most stable among the NM₄ clusters. The high stability and tetrahedral geometry make these species idea units for building new materials.     

Lattice dynamics and electronic structure of cobalt–titanium spinel Co2TiO4

Physics of the Solid State - The results are presented on phonon excitations and the electronic structure of Co2TiO4 inverse spinel in which magnetically ordered cobalt ions Co2+ (3d 7) are in...     

Investigation of structural and electronic properties of β- HgS: Molecular dynamics simulations

The pressure induced phase transition of β-HgS is studied using an ab initio molecular dynamics simulation. The structural phase transformation from the zinc-blende structure to the NaCl-type structure (space group $Fm\overline{3}m$) and from this structure to CsCl-type structure ($Pm\overline{3}m$) with the application of hydrostatic pressure is predicted. Additionally, the electronic properties of HgS and various physical properties such as the lattice constants, the bulk modulus and the pressure derivative of the bulk modulus are revealed. Furthermore, these phase transitions are obtained using the total energy and enthalpy calculations. According to these calculations these transformations are occurring at about 20?GPa and 28?GPa for $F\overline{4}3m$ →$Fm\overline{3}m$ and $Fm\overline{3}m$ →$Pm\overline{3}m$, respectively.     

Ab initio study of structural,electronic, and elastic properties of M<Subscript>2</Subscript>SbP (M = Ti,Zr, and Hf)

This study predicts the structural behaviour of selected M₂SbP compounds with the same structure as MAX phases. Zero pressure results of the lattice parameters, equilibrium volume, and the internal parameter Z_M are calculated with an error less than 3%. Band structure, total and partial density of states were calculated and show the metallic character of these phases. Moreover we observed strong hybridising states; M d–P p, and M d–Sb p. The pressure dependence of the volume, and the lattice parameters were studied. The stiffness of M–P, and M–Sb bonds was discussed in term of relative length change under hydrostatic pressure. Hf₂SbP present the highest bulk modulus and the unidirectional elastic modulus C₃₃ is slightly greater than C₁₁.     

Structural,elastic and optoelectronic properties of Sr-based perovskite-type oxides SrXO3 (M = Th,Zr) via first-principles calculations

In this paper, we present a detailed theoretical investigation on the structural, elastic, electronic and optical properties of the perovskite oxides SrThO₃ and SrZrO₃ by using the pseudo-potential plane wave (PP-PW) method. The computed lattice constants of SrXO₃ (X = Th and Zr) are in excellent agreement with the available experimental data. SrThO₃ and SrZrO₃ are direct (Γ–Γ) and indirect (Γ–R) band gap semiconductors, respectively. Under pressure effect a crossover between the indirect band gap (R–Γ) and the direct band gap (Γ–Γ) curves occurs at about 35 GPa for SrZrO₃, resulting in the energy minimum of direct gap (Γ–Γ) for this compound. The covalence in the Zr–O and Th–O bonds arises due to the hybridization between O–p and Zr–d (Th–d) states. Under pressure effect, the threshold energy becomes slightly greater (smaller) for SrZrO₃ (SrTO₃) for 3.21 (2.28) eV and the main peaks are shifted towards higher energies. Although the positions of all peaks shifted under pressure, they still have the same type as those at zero pressure, with decreasing the intensity of the main peaks.     

Investigations of half-metallic ferromagnetism and thermoelectric properties of cubic XCrO3 (X = Ca,Sr,Ba) compounds via first-principles approaches

In this paper, the physical aspects of the cubic phase XCrO₃ ($\mathrm{X}=\mathrm{Ca},\mathrm{Sr},\mathrm{Ba}$) perovskites are studied by employing full-potential linearized augmented plane wave plus local orbital ($\text{FP-LAPW}+\mathit{lo}$) method. These compounds have been found stable in ferromagnetic (FM) phase since they possess lower energy in FM phase compared to non-FM phase and their stability is also confirmed by calculating the enthalpy of formation (ΔH). The electronic structures of these compounds are analyzed with Trans and Blaha modified Becke–Johnson potential (TB-mBJ) for both spin up and spin down channels, which indicate their half-metallic characters. Analysis of density of states (DOS) shows major contributions of O-2p states in the valence band and Cr 3d-state in conduction band. A comparative analysis of crystal field effect ($\mathrm{\Delta }{\mathrm{E}}_{\mathrm{crystal}}$) and the exchange energies (direct ${\mathrm{\Delta }}_x(d)$ and indirect ${\mathrm{\Delta }}_x(pd)$) tells about the main part of electronic spin in ferromagnetic character. The calculated magnetic moments make these compounds favorable for spintronic applications. In the end, thermoelectric parameters are computed for 200 K–800 K temperature range to explore potential of these compounds for applications in renewable energy devices.     

Ab-initio study of structural,electronic, elastic and mechanical properties of RuAl1−xGax (x=0, 0.25, 0.50, 0.75 and 1)

We have used special quasirandom structure to study the structural, electronic, elastic and mechanical properties of RuAl_1−xGa_x alloys for different compositions (x=0, 0.25, 0.50, 0.75 and 1) using a FP-LAPW method based on Density Functional Theory. The exchange and correlation potential is treated within the generalized gradient approximation. Ground state properties such as lattice constant (a₀), bulk modulus (B), its pressure derivative (B′) and elastic constants are calculated. The ductility of these alloys has been analyzed by calculating the ratio of B/G_H, Cauchy pressure (C₁₂–C₄₄) and Frantsevich rule. From this study RuAl and RuGa are found to be brittle, but their alloys show ductile behavior; RuAl_0.50Ga_0.50 is found to be most ductile. Mechanical properties such as Poisson's ratio (σ), Young's moduli (E), and the ratio of elastic anisotropy factor (A) are estimated. We have also correlated the ductility and bonding behavior of these alloys.     

Density functional theory studies on the electronic, structural, phonon dynamical and thermo-stability properties of bicarbonates MHCO(3), M?=??Li, Na, K

The structural, electronic, phonon dispersion and thermodynamic properties of MHCO(3) (M = Li, Na, K) solids were investigated using density functional theory. The calculated bulk properties for both their ambient and the high-pressure phases are in good agreement with available experimental measurements. Solid phase LiHCO(3) has not yet been observed experimentally. We have predicted several possible crystal structures for LiHCO(3) using crystallographic database searching and prototype electrostatic ground state modeling. Our total energy and phonon free energy (F(PH)) calculations predict that LiHCO(3) will be stable under suitable conditions of temperature and partial pressures of CO(2) and H(2)O. Our calculations indicate that the [Formula: see text] groups in LiHCO(3) and NaHCO(3) form an infinite chain structure through O?H?O hydrogen bonds. In contrast, the [Formula: see text] anions form dimers, [Formula: see text], connected through double hydrogen bonds in all phases of KHCO(3). Based on density functional perturbation theory, the Born effective charge tensor of each atom type was obtained for all phases of the bicarbonates. Their phonon dispersions with the longitudinal optical-transverse optical splitting were also investigated. Based on lattice phonon dynamics study, the infrared spectra and the thermodynamic properties of these bicarbonates were obtained. Over the temperature range 0-900 K, the F(PH) and the entropies (S) of MHCO(3) (M =Li, Na, K) systems vary as F(PH)(LiHCO(3)) > F(PH)(NaHCO(3)) > F(PH)(KHCO(3)) and S(KHCO(3)) > S(NaHCO(3)) > S(LiHCO(3)), respectively, in agreement with the available experimental data. Analysis of the predicted thermodynamics of the CO(2) capture reactions indicates that the carbonate/bicarbonate transition reactions for Na and K could be used for CO(2) capture technology, in agreement with experiments.