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.     

Elastic and thermodynamic properties of alkali hydrides XH (X = K,Rb and Cs)

The calculation of the structural, mechanical and thermodynamic properties of the alkali hydrides XH (X?=?K, Rb and Cs) in rock-salt (RS), cesium chloride (CsCl), zinc-blende (ZB) and wurtzite (WZ) phases are done by using the full-potential linearized augmented plane wave (FP-LAPW) method within the frame work of the density functional theory (DFT) as implemented in the WIEN2K code. The Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) was used for the exchange-correlation potential.The elastic constants and their related properties, as well as the thermodynamic properties, were obtained by using the IRelast package. The calculated elastic constants for the alkali hydrides, with the four structures RS, CsCl, ZB and WZ, at ambient pressure are mechanically stable. The elastic constants and their related properties in the RS structure are changeable with increasing pressure. Elastic constants, bulk modulus, shear modulus (stiffness) and Debye temperatures of these compounds are decreased as going from K to Cs in the periodic table. These compounds in the RS structure are mechanically stronger at ambient conditions.     

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.     

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.     

Structural,electronic, optical and thermodynamic investigations of NaXF3 (X = Ca and Sr): First-principles calculations

The structural, electronic and optical properties for fluoro-perovskite NaXF₃ (X?=?Ca and Sr) compounds have calculated by WIEN2k code based on full potential linearized augmented plane wave (FP-LAPW) approach within density functional theory (DFT). To perform the total energy calculations, exchange-correlation energy/potential functional has been utilized into generalized gradient approximation (GGA) and local density approximation (LDA). Our evaluated results like equilibrium lattice constants, bulk moduli, and their pressure derivatives are in agreement with the available data. The electronic band structure calculation has revealed an indirect band-gap nature of NaCaF₃, while NaSrF₃ has direct band gap. Total and partial densities of states confirm the degree of localized electrons in different bands. The optical transitions in NaCaF₃ and NaSrF₃ compounds were identified by assigning corresponding peaks obtained from the dispersion relation for the imaginary part of the dielectric function. The thermodynamic properties were calculated using quasi-harmonic Debye model to account lattice vibrations. In addition, the influence of temperature and pressure effects was analyzed on bulk modulus, lattice constant, heat capacities and Debye temperature.     

Computational investigations of mechanical and dynamical properties of gold-based compounds (X3Au,X = Ti,Zr and V)

The structural, elastic, electronic and phonon properties of X₃Au (X?=?Ti, Zr and V) compounds in the A15 structure were obtained in the framework of the density functional theory (DFT) within the generalized gradient approximation (GGA). The equilibrium lattice constants, bulk modulus and elastic constants were calculated. The calculation of elastic constants revealed that V₃Au has the highest hardness nature and incompressibility along the x-axis among them. The computed elastic constants also provided information about the ductility of X₃Au compounds which were predicted using Pugh's criteria. The results indicated that all three compounds have ductile nature. The density of states calculations revealed that electrons of Ti, Zr and V provide most contribution to the conductivity of the compounds and thus cause a metallic bonding. The investigation of stability via phonon spectra of compounds showed that these compounds are dynamically stable in the A15 structure.     

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.     

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.     

Magnetic moment collapse induced by high-pressure in semi-borides TM2B (TM = Fe,Co). A first-principles study

The high-pressure effects are investigated on the structure, magnetic phase transition, and anisotropic elastic properties of the 3d transition-metal semi-borides TM₂B (TM?=?Fe, Co) by using the generalized gradient approximation (GGA) within the framework of density functional theory (DFT). At equilibrium spin polarization, calculations show that the Fe₂B and Co₂B compounds are ferromagnetic (FM). In the applied pressure range from 0 to 90?GPa, the magnetic moment of Fe₂B and Co₂B slowly decreases and then abruptly drops to zero at 85?GPa, indicating a state transition from the ferromagnetic to the nonmagnetic (NM) state (a first-order quantum phase transition). The collapse of the magnetic moment is accompanied by an abrupt change in the lattice parameters and elastic constants. In addition to this phenomenon, the density of states (DOS), and anisotropic elastic properties are presented at 0?GPa and at the critical transition pressure. Furthermore, I have plotted the three-dimensional (3D) surfaces and planar contours for the Young and bulk moduli of the compounds at several crystallographic planes, ((100) and (001)) to reveal their elastic anisotropy. On the basis of anisotropic elastic properties, I have predicted the easy and hard axes of magnetization for the TM₂B compounds.     

Structural and electronic properties of SbnAl(0,±1) (n = 1–10) clusters using density-functional theory

We used the density functional theory (DFT) with the unrestricted B3LYP exchange-correlation potential and LanL2DZ basis sets to optimize the geometries of Sb_nAl and Sb_nAl^±1 (n = 1–10) clusters. We mainly utilized Gaussian 03 W software to calculate the data. In order to find the most stable structure of each isomer, we calculated the total energy, the spin multiplicity (S), point group symmetry (PG), the electronic state (State), and the average bond lengths of Sb-Al bond and Sb-Sb bond (R₁ and R₂). Through the calculations and analysis of these data, we found the ground state structure of each group isomer. By discussing the average binding energy (E_b), fragmentation energy (E_f), and the second-order energy difference (Δ₂E), the stabilities of the Sb_nAl ^(0,±1) clusters were studied. The results of the electron transfer show that the Sb₄Al and Sb₈Al clusters are different with the other neutral clusters. In order to study the electric properties of Sb_nAl ^(0,±1) clusters, the energy gap (E_g) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), AEA, VDE, AIP, and VIP were calculated. Besides, the magnetic moment of the positive and negative clusters have the same effects when n = 2–9.     

Electronic,optical and thermoelectric investigations of Zintl phase AE3AlAs3 (AE = Sr,Ba): First-principles calculations

First principles calculations were performed to investigate the electronic, optical and thermoelectric properties of Zintl orthorhombic phase AE₃AlAs₃ (AE?=?Sr, Ba) compounds using the full potential linearized augmented plane wave method. The exchange-correlation potential is treated with the generalized gradient approximation (GGA) and modified Becke-Johnson potential (TB-mBJ) to improve the electronic structure calculations. These two compounds are semiconductors have direct band gaps. The optical transitions are investigated via dielectric function along with other related optical constants such as refractive index and absorption coefficient. Thermoelectric properties are examined using the combination of electronic structure and Boltzmann transport theory. In detail, the calculated results of Seebeck coefficient, electrical and thermal conductivity, figure of merit and power factor are reported as a function of temperature.     

Phase stability,electronic, magnetic and elastic properties of Ni2CoZ(Z = Ga,Sn): A first principles study with GGA method and GGA+U approach

First principles calculations based on density functional theory are used to investigate the phase stability, electronic, magnetic and elastic properties of ferromagnetic metallic full-Heusler Ni₂CoZ(Z = Ga, Sn) alloys via the FP-LAPW method by the generalized gradient GGA and GGA+U approximations for the exchange and correlation energy, within the Perdew–Burke–Ernzerhof (PBE 96) parameterization. The results of calculating electronic structures and magnetic properties reveal that the both Ni₂CoGa and Ni₂CoSn crystallize in L2₁ phase with regular cubic structure. The two investigated compounds exhibit metallic ferromagnetic behaviors for the GGA+U calculation. The computation of elastic constants with GGA+U approach shows that our compounds are mechanically stable.     

First-principle study of the electronic,magnetic and structural characteristics of the Mn2CoAs1−xAlx (x = 0,0.25,0.50,0.75) Heusler alloys

First-principles density functional theory approach is adopted to determine the electronic, magnetic and structural characteristics of the Mn₂CoAs_1−xAl_x (x = 0,0.25,0.50,0.75) Heusler alloys. The computations are carried out by WIEN2k code based on full-potential linearized augmented plane wave method (FP-LAPW). Moreover, the exchange-correlation energy functional is treated at the level of the generalized gradient approximation (GGA). Analysis of our computed results of the electronic band structure, as well as the density of states of the Mn₂CoAs compound, show it a stable and half-metallic material with an energy band gap value of 0.48 eV. The calculated spin gap values are: 0.627 eV, 0.22 eV and 0.188 eV for Mn₂CoAs_0.75Al_0.25, Mn₂CoAs_0.50Al_0.50 and Mn₂CoAs_0.25Al_0.75 respectively. Furthermore, the calculated total magnetic moment of the Mn₂CoAs (4 µB) is found to be in agreement with the Slater–Pauling rule. Thus, our calculations show the Mn₂CoAs_1−xAl_x (x = 0, 0.25, 0.50, 0.75) Heusler alloys potential materials for near future applications in spintronic because of their half-metallic ferromagnetism property.     

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.     

First principles study on structural,electronic and optical properties of Ga1−xBxP ternary alloys (x = 0, 0.25, 0.5, 0.75 and 1)

The structural, electronic and optical properties of GaP, BP binary compounds and their ternary alloys Ga_1?xB_xP ($x=0.25$, 0.5 and 0.75) have been studied by full-potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT) as implemented in WIEN2k package. Local density approximation (LDA) and generalized gradient approximation (GGA) as proposed by Perdew–Burke–Ernzerhof (PBE), Wu–Cohen (WC) and PBE for solid (PBESol) were used for treatment of exchange-correlation effect in calculations. Additionally, the Tran–Blaha modified Becke–Johnson (mBJ) potential was also employed for electronic and optical calculations due to that it gives very accurate band gap of solids. As B concentration increases, the lattice constant reduces and the energy band gap firstly decreases for small composition x and then it shows increasing trend until pure BP. Our results show that the indirect–direct band gap transition can be reached from $x=0.33$. The linear optical properties, such as reflectivity, absorption coefficient, refractive index and optical conductivity of binary compounds and ternary alloys were derived from their calculated complex dielectric function in wide energy range up to 30 eV, and the alloying effect on these properties was also analyzed in detail.     

The hydrogen atom in D = 3 − 2ϵ dimensions

The nonrelativistic hydrogen atom in $D=3?2?$ dimensions is the reference system for perturbative schemes used in dimensionally regularized nonrelativistic effective field theories to describe hydrogen-like atoms. Solutions to the D-dimensional Schrödinger–Coulomb equation are given in the form of a double power series. Energies and normalization integrals are obtained numerically and also perturbatively in terms of ?. The utility of the series expansion is demonstrated by the calculation of the divergent expectation value $〈{(V^{\prime })}^2〉$.     

Study of the structural,elastic, electronic and optical properties of lead free halide double perovskites Cs2AgBiX6(X = Br,Cl)

The lead free halides double perovskites show a particular interest in the conception of perovskites solar cells. We predicted the lattice constant and the atomic Wycko position of these lead free halide double perovskites Cs₂AgBiX₆ (X?=?Br, Cl) under pressure effect. The alloying ability of crystal, elastic constants and related parameters, electronic and optical properties have been studied using pseudo potential plane wave method based on the density functional theory. The investigated lead free halide double perovskites Cs₂AgBiX₆ (X?=?Br, Cl) show a weaker resistance to compression along the a-axis. This result also proves the existence of a directional bonding between atoms and a weaker resistance to compression along the a-axis The band structure indicates that Cs₂AgBiX(X?=?Br, Cl) are X–L indirect gap semiconductors. Our computed bulk modulus and its pressure derivative of double perovskites Cs₂AgBiX₆ (X?=?Br, Cl) are predictions. The calculated elastic constants of Cs₂AgBiX₆ (X?=?Br, Cl) at equilibrium and under pressure effect are predictions.     

发射光谱法测定高纯银中微量金,铂,钯,铑,铱,锑,铅,铋,铁,铜,…

本文研究了贵金属标准溶液除氯离子的有关问题，解决了高纯硝酸银中贵金属等杂质元素的样配制，以硝酸银直接压样于普通电极中直流电弧激发，可测定９９．０－９９．９９％的高纯银，该方法简便、快速、准确。     

锰结核中硅,铝,铁,镁,磷,钾,锰,钛的XRFA

本文叙述了用XRF分析锰结核中Si、Al、Fe、Mg、P、K、Mn和Ti的方法。按照通常锰结核的主次成分制备6个人工合成标准,根据Sherman方程计算了已知成分(二元系统)的相对强度。用L-T方求得了互致元素校正的理论α系数(基本的、混合的、修正的),用DATAFLEX151B计算机以BASIC语言汇了“PRA,APU”计算机程序。然后进行非线性回归分析了锰结核样品得到了满意的结果。