First-principles study of the structural, elastic, electronic, optical, and vibrational properties of intermetallic Pd2Ga

The structural,elastic,electronic,optical,and vibrational properties of the orthorhombic Pd2Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory.The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results.The second-order elastic constants and the other relevant quantities,such as the Young’s modulus,shear modulus,Poisson’s ratio,anisotropy factor,sound velocity,and Debye temperature,have been calculated.It is shown that this compound is mechanically stable after analysing the calculated elastic constants.Furthermore,the real and imaginary parts of the dielectric function and the optical constants,such as the optical dielectric constant and the effective number of electrons per unit cell,are calculated and presented.The phonon dispersion curves are derived using the direct method.The present results demonstrate that this compound is dynamically stable.     

Fluid-structure coupling in the guitar box: numerical and experimental comparative study

Resonance boxes are common to many musical instruments and determine the radiated sound to a great extent. The behaviour of the structure and the air inside must be understood as a whole, the complexity of which is increased by the presence of sound holes. In this work, we present a comparative study of the guitar box in which the interior gas is changed both experimentally and numerically. Modal patterns, natural frequencies and quality factors are determined when the box is full of helium, air and krypton, respectively. This allows us to characterise the soundboard-back plate coupling via the cavity fluid, stressing the role of the structural and acoustic uncoupled modes. This could help guitar makers, allowing them to modify the final modes by means of structural modifications. Moreover the methodology, together with the developed finite element model, proves to be valid for studying the dynamic fluid-structure coupling in any arbitrary mechanical system, including cavities connected to the surrounding air.     

First-principles study of the structural, elastic, electronic, optical, and vibrational properties of intermetallic Pd2Ga

The structural, elastic, electronic, optical, and vibrational properties of the orthorhombic Pd₂Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory. The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results. The second-order elastic constants and the other relevant quantities, such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocity, and Debye temperature, have been calculated. It is shown that this compound is mechanically stable after analysing the calculated elastic constants. Furthermore, the real and imaginary parts of the dielectric function and the optical constants, such as the optical dielectric constant and the effective number of electrons per unit cell, are calculated and presented. The phonon dispersion curves are derived using the direct method. The present results demonstrate that this compound is dynamically stable.     

Synthesis,spectroscopic and structural characterisation of two p-nitrobenzamide compounds: experimental and DFT study

The title molecules, N-(1,5-dimethyl-3-oxo-2-phenyl-1H-3-(2H)-pyrazolyl)4-nitrobenzamide (C₁₈H₁₆N₄O₄·H₂O) (I) and 2,2-dimethyl-3-(4-nitrobenzoyl)-5-(phenylamino)-2,3-dihydro-1,3,4-thiyadiazole (C₁₇H₁₆N₄O₃S) (II), were prepared and characterised by ¹H NMR, ¹³C NMR, infrared spectroscopy (IR) and structural X-ray diffraction (XRD) techniques. The molecular geometries, vibrational frequencies of the title compounds in the ground state have been calculated by using the density functional theory (DFT) method with 6-31G(d) basis set, and compared with the experimental data. The calculated results showed that the optimised geometries from the DFT method agree with the X-ray structures well for both compounds. Theoretical calculations of harmonic vibration frequencies are in good agreement with experimental results. To determine conformational flexibility, the molecular energy profiles of the title compounds were obtained. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis and thermodynamic properties of the title compounds were investigated by theoretical calculations.     

Ultrasonic-assisted manufacturing processes: variational model and numerical simulations

We present a computational study of ultrasonic assisted manufacturing processes including sheet metal forming, upsetting, and wire drawing. A fully variational porous plasticity model is modified to include ultrasonic softening effects and then utilized to account for instantaneous softening when ultrasonic energy is applied during deformation. Material model parameters are identified via inverse modeling, i.e. by using experimental data. The versatility and predictive ability of the model are demonstrated and the effect of ultrasonic intensity on the manufacturing process at hand is investigated and compared qualitatively with experimental results reported in the literature.     

Theoretical study of the SrLi+ molecular ion: structural,electronic and dipolar properties

ABSTRACT

The structural and electronic properties of (SrLi)⁺ molecular ion have been determined by the use of ab initio approaches. Potential energy curves (PECs) with their spectroscopic constants (R_e, D_e, ω_e, T_e, B_e and ω_eχ_e) have been calculated. Also, the vibrational properties and the electric dipole moments, either permanent (PDM) or transition (TDM) ones, have been investigated and analysed. Large Gaussian basis sets, the full valence configuration interaction (FCI) and the formalism of non-empirical pseudo-potential including the two approaches, effective core potential (ECP) and core polarisation potential (CPP), are analysed. Therefore, (SrLi)⁺ is considered as a two effective electrons system. Numerous excited states of symmetries ^1,3Σ⁺, ^1,3Π and ^1,3Δ dissociating below the ionic limit Sr²⁺Li^? have been investigated. This study shows interesting behaviours around the avoided crossing related to charge transfer involving important processes in physics and astrophysics such as dynamics, pre-dissociation and inelastic transitions.     

包膜黏弹特性及声驱动参数对相互作用微泡动力学行为的影响

关于多气泡相互作用的理论研究对于深入理解超声造影剂在医疗领域中的应用机理具有重要意义。本工作建立了一个2维轴对称有限元模型来研究流体环境中超声造影剂双气泡相互作用,讨论了驱动超声频率和气泡尺寸对气泡之间吸引和排斥趋势的影响,得到了气泡半径与气泡之间距离随时间变化的曲线,以及气泡周围流体速度场的细节,并且研究了气泡包膜参数(即表面张力系数和粘度系数)对气泡相互作用的影响.结果表明,相互作用中的气泡对整体的相对运动趋势由驱动频率和共振频率之间的关系决定;在超声参数固定时,气泡包膜的粘弹特性可用来调控气泡间相互作用强度。结果对实验中观察到的气泡聚集现象进行了合理解释,并为超声造影剂在医疗实践中的应用提供了基础理论支撑.     

Insights into structural,electronic, optical and thermoelectric properties of WB and WAlB: a first principle study

Detailed investigations on structural, electronic, optical and thermoelectric properties of WB and WAlB have been done by using a full-potential linearised augmented plane wave method. Different approximations have been used to treat the exchange–correlation potential. The PBEsol-GGA method is found to be the most suitable for WB and WAlB. The obtained values of the equilibrium structural parameters such as lattice constants, volume and bulk modulus are in good agreement with the available experimental and theoretical data. The results of electronic charge density plots show that WB has a strong covalent bond between B-B and an ionic bond between W-B. In case of WAlB, the distance between any two atoms is more than the corresponding interatomic distance in WB. The band structure and density of states around the fermi level suggest that WB has a metallic nature and WAlB has a semimetal-like character. The optical properties are determined and analysed in detail for the first time. The larger reflectivity in the low-energy region (infrared) indicates that these materials can be used as a coating material to remove solar heating. The effects of temperature on thermoelectric parameters are also studied for the first time. High value power factor and high thermal conductivity suggest that WB and WAlB are potential candidates for thermoelectric technological applications.     

Vibrational spectra and structural studies of nonlinear optical crystal ammonium D,L‐tartrate: a density functional theoretical approach

Single crystals of ammonium D , L ‐tartrate, a potential nonlinear optical (NLO) material of interest, were grown by the slow evaporation technique. The crystal structure was determined by single‐crystal X‐ray diffraction. Fourier transform infrared and Raman spectra of the crystallized molecule were recorded and analyzed. The geometry, intermolecular hydrogen bonding, first hyperpolarizability and harmonic vibrational wavenumbers were calculated with the help of B3LYP density functional theory method. The red shift of hydroxyl and NH₄⁺ stretching wavenumbers indicate the formation of inter‐ and intramolecular hydrogen bonding. Simultaneous activation of CH stretching wavenumbers shows the presence of intramolecular charge transfer in the molecule. Natural bond orbital analysis was carried out to demonstrate the various inter‐ and intramolecular interactions that are responsible for the stabilization of this molecule, leading to high NLO activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of the electric field behavior in the vicinity of a triple junction,using finite elements method computational simulations

The authors studied the electric field behavior in the vicinity of a triple junction, composed by metal, vacuum and dielectric parts, using computational simulations. A bi-dimensional model was constructed using ANSYS MAXWELL to analyze the magnitude of the electric field as a function of the contact angles of the materials. The results showed that a field enhancement or reduction could occur in vacuum for certain contact angles. The influence of the dielectric permittivity was also investigated, and the conclusions showed that the maximum electric field enhancement is proportional to the dielectric permittivity.     

Ab initio study of the structural,electronic, elastic and thermal conductivity properties of SrClF with pressure effects

Abstract

SrClF is an important optical crystal and can be used as pressure gauge in diamond anvil cell at high pressure. In this work, we performed a systematic study on the structural, electronic and elastic properties of SrClF under pressure, as well as its thermal conductivity, by first-principles calculation. Different exchange-correlation functionals were tested and PBESOL was finally chosen to study these properties of SrClF. Studies reveal that SrClF has a bulk modulus of about 56.2 GPa (by fitting equation of states) or 54.3 GPa (derived from elastic constants), which agree well with the experimental result. SrClF is mechanically and dynamically stable up to 50 GPa. Its elastic constants increase with the applied pressure, but its mechanical anisotropy deteriorates as the pressure increases. Investigation of its electronic properties reveals that SrClF is a direct band-gap insulator with a gap value of 5.73 eV at 0 GPa, which decreases with the increasing pressure and the reason is found by analysing the partial density of states. Based on the calculated phonon dispersion curves, thermal conductivity of SrClF is predicated. At ambient conditions, the predicted thermal conductivity is about 3.74 Wm^?1 K^?1, while that obtained using the simplified Slack model give a slightly larger value of 4.62 Wm^?1 K^?1.     

First-principles study of the structural,electronic, and magnetic properties of double perovskite Sr_2FeReO_6 containing various imperfections

The structural, electronic, and magnetic properties of double perovskite Sr_2FeReO_6 containing eight different imperfections of FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, V_(Fe), V_(Re), VOor V_(Sr) vacancies have been studied by using the first-principles projector augmented wave(PAW) within generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction(GGA+U). No obvious structural changes are observed for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges, or VSrvacancy defects. However, the six(eight) nearest oxygen neighbors of the vacancy move away from(close to) VFeor V_(Re)(VO) vacancies. The half-metallic(HM) character is maintained for the imperfect Sr_2FeReO_6 containing FeReor ReFeantisites, Fe1–Re4 interchange, V_(Fe),VO or V_(Sr) vacancies, while it vanishes when the Fe1–Re1 interchange or VRevacancy is presented. So the Fe1–Re1 interchange and the VRevacancy defects should be avoided to preserve the HM character of Sr_2FeReO_6 and thus usage in spintronic devices. In the FeReor ReFeantisites, Fe1–Re1 or Fe1–Re4 interchanges cases, the spin moments of the Fe(Re)cations situated on Re(Fe) antisites are in an antiferromagnetic coupling with those of the Fe(Re) cations on the regular sites. In the V_(Fe), V_(Re), VO, or V_(Sr) vacancies cases, a ferromagnetic coupling is obtained within each cation sublattice,while the two cation sublattices are coupled antiferromagnetically. The total magnetic moments μtot(μB/f.u.) of the imperfect Sr_2FeReO_6 containing eight different defects decrease in the sequence of VSrvacancy(3.50), VRevacancy(3.43),FeReantisite(2.74), VOvacancy(2.64), VFevacancy(2.51), ReFeantisite(2.29), Fe1–Re4 interchange(1.96), Fe1–Re1interchange(1.87), and the mechanisms of the saturation magnetization reduction have been analyzed.     

Dark-bright discrete solitons: A numerical study of existence, stability and dynamics

In the present work, we numerically explore the existence and stability properties of different types of configurations of dark-bright solitons, dark-bright soliton pairs and pairs of dark-bright and dark solitons in discrete settings, starting from the anti-continuum limit. We find that while single discrete dark-bright solitons have similar stability properties to discrete dark solitons, their pairs may only be stable if the bright components are in phase and are always unstable if the bright components are out of phase. Pairs of dark-bright solitons with dark ones have similar stability properties as individual dark or dark-bright ones. Lastly, we consider collisions between dark-bright solitons and between a dark-bright one and a dark one. Especially in the latter and in the regime where the underlying lattice structure matters, we find a wide range of potential dynamical outcomes depending on the initial soliton speed.     

Pressure effect on structural,electronic optical and thermodynamic properties of cubic AlxIn1-xP: a first-principles study

ABSTRACT

First-principles total energy calculations have been performed using the full potential linearised augmented plane wave (FP-LAPW) method as implemented in the WIEN2k code based on the density functional theory (DFT) to investigate the Al-doping effects on the structural, electronic and optical properties of Al_xIn_1-xP ternary alloys in the zinc-blende (ZB) phase. Different approximations of exchange-correlations energy were used such as the local density approximation (LDA), the generalised gradient approximation within parameterisation of Perdew–Burke–Ernzerhof (PBE-GGA), and the Wu-Cohen (WC-GGA). In addition, we have calculated the band structures with high accuracy using the Tran-Blaha modified Becke–Johnson (TB-mBJ) approach. The pressure dependence of the electronic and optical properties of binary AlP, InP compounds and their related ternary alloys Al_xIn_1-xP were also investigated under hydrostatic pressure for (P?=?0.0, 5.0,10.0, 15.0, 20.0, 25.0?GPa), where it is found that InP compound change from direct to indirect band gap for P?≥?9.16?GPa. Furthermore, we have calculated the thermodynamic properties of InP and AlP binary compounds as well as the Al_xIn_1-xP solid solutions, where the quasi-harmonic Debye model has been employed to predict the pressure and temperature dependent Gibbs free energy, heat capacity, Debye temperature and entropy.     

A first-principles study on the structural, lattice dynamical and thermodynamic properties of beryllium chalcogenides

First-principles calculations, which are based on the plane-wave pseudopotential approach to the density functional theory and the density functional perturbation theory within the local density approximation, have been performed to investigate the structural, lattice dynamical and thermodynamic properties of zinc blende (B3) structure beryllium chalcogenides: BeS, BeSe and BeTe. The results of ground-state parameters and phonon dispersion are compared and contrasted with the experimental and theoretical data of previous literature. The phonon frequencies at the zone-center are analyzed. We also used the phonon density of states and quasiharmonic approximation to calculate and predict some thermodynamic properties such as entropy, heat capacity, internal energy and free energy of the B3 phase beryllium chalcogenides.     

高压下RhB的相变、弹性性质、电子结构及硬度的第一性原理计算

采用密度泛函理论中的赝势平面波方法系统地研究了高压下RhB的结构相变、弹性性质、电子结构和硬度.分析表明,RhB在25.3 GPa时从anti-NiAs结构相变到FeB结构,这两种结构的弹性常数、体弹模量、剪切模量、杨氏模量和弹性各向异性因子的外压力效应明显.电子态密度的计算结果显示,这两种结构是金属性的,且费米能级附近的峰随着压强的增大向两侧移动,赝能隙变宽,轨道杂化增强,共价性增强,非局域化更加明显.此外,硬度计算结果显示,anti-NiAs-RhB的金属性比较弱,有着较高的硬度,属于硬质材料.     

First principle study of the structural and optoelectronic properties of cubic perovskites CsPbM3 (M=Cl, Br, I)

The highly accurate all electrons full potential linearized augmented plane wave method is used to calculate structural, electronic, and optical properties of cubic perovskites CsPbM₃ (M=Cl, Br, I). The theoretically calculated lattice constants are found to be in good agreement with the experimentally measured values. It is found that all of these compounds are wide and direct bandgap semiconductors with bandgap located at R-symmetry point, while the bandgap decreases from Cl to I. The electron densities reveal strong ionic bonding between Cs and halides but strong covalent bonding between Pb and halides. Optical properties of these compounds like real and imaginary parts of dielectric functions, refractive indices, extinction coefficients, reflectivities, optical conductivities, and absorption coefficients are also calculated. The direct bandgap nature and high absorption power of these compounds in the visible-ultraviolet energy range imply that these perovskites can be used in optical and optoelectronic devices working in this range of the spectrum.     

Structural conformations and electronic interactions of the natural product,oroxylin: a vibrational spectroscopic study

The oroxylin, 5,7‐dihydroxy 6‐methoxy flavone is a potent natural product extracted from ‘Vitex peduncularis’. Density functional theory (DFT) at B3LYP/6‐311G(d,p) level has been used to compute energies of different conformers of oroxylin to find out their stability, the optimized geometry of the most stable conformer and its vibrational spectrum. The conformer ORLN‐1 with torsion angles 0, 180, 180 and 0 degrees, respectively, for H₁₃ O₁₂ C₆ C₅, H₁₄ O₁₀ C₄ C₅, H₁₃ O₁₂ C₆ C₅ and H₁₄ O₁₀ C₄ C₅ is found to be most stable. The optimized geometry reveals that the dihedral angle φ between phenyl ring B and the chrome part of the molecule in − 19.21° is due to the repulsive force due to steric interaction between the ortho‐hydrogen atom H₂₉ of the B ring and H₁₈ of the ring C (H₂₉·H₁₈ = 2.198 Å). A vibrational analysis based on the near‐infrared Fourier transform(NIR‐FT) Raman, Fourier transform‐infrared (FT‐IR) and the computed spectrum reveals that the methoxy group is influenced by the oxygen lone pair‐aryl p_z orbital by back donation. Hence the stretching and bending vibrational modes of the methoxy group possess the lowest wavenumber from the normal values of methyl group. The carbonyl stretching vibrations have been lowered due to conjugation and hydrogen bonding in the molecules. The intramolecular H‐bonding and nonbonded intramolecular interactions shift the band position of O₁₀ H₁₄ and O₁₂ H₁₃ stretching modes, which is justified by DFT results. Copyright © 2008 John Wiley & Sons, Ltd.     

A first-principles study on the structural, elastic, vibrational, and thermodynamical properties of BaX (X=S, Se, and Te)

Ab-initio calculations based on norm-conserving pseudopotentials and density functional theory (DFT) have been performed to investigate the structural, elastic, thermodynamic, and lattice dynamical (phonon dispersion curves) properties of BaX in rock-salt (B1) and CsCl (B2) structures. The results support the experimental and theoretical data in the existing literature. Findings are also presented for the temperature-dependent behaviors of some thermodynamic properties such as entropy, heat capacity, internal energy, and free energy for the same compounds in the B1 phase.