First-principles investigation of structural, electronic, optical and dynamical properties in CsAu

The structural, electronic, optical and dynamical properties of CsAu compound in the CsCl(B2) phase were investigated using the density functional theory (DFT) within the generalized gradient approximation (GGA). The calculated lattice constant, static bulk modulus and first-order pressure derivative of the bulk modulus are reported and compared with previous experimental and theoretical calculations. The calculated electronic band structure for this compound is in good agreement with available theoretical and experimental studies. The present band calculation indicates that CsAu compound has an indirect gap at R→X points. Furthermore, the linear photon-energy-dependent dielectric functions have been calculated. For the first time, the electronic structure results are used, within the implementation of a linear-response technique, for calculations of phonon properties.     

Phase transition and bulk properties of some polonide compounds: a comparative study

In the present paper the structural and electronic properties of polonides of lead, barium and calcium polonide (PbPo, BaPo and CaPo) have been reported. These properties have been studied using first principles calculations as well as the interionic potential model modified with the covalency effect. Gibbs free energy and enthalpy calculations show that these compounds undergo a structural phase transition from NaCl-type structure to CsCl-type structure. The electronic band structure and density of states of the PbPo, BaPo and CaPo have also been reported. The calculated equilibrium structural parameters are in good agreement with the available experimental results.     

Structural, electronic and optical properties of AgI under pressure

We report results of first-principles total-energy calculations for structural properties of the group I-VII silver iodide (AgI) semiconductor compound under pressure for B1 (rocksalt), B2 (cesium chloride), B3 (zinc-blende) and B4 (wurtzite) structures. Calculations have been performed using all-electron full-potential linearized augmented plane wave plus local orbitals FP-LAPW + lo method based on density-functional theory (DFT) and using generalised gradient approximation (GGA) for the purpose of exchange correlation energy functional. In agreement with experimental and earlier ab initio calculations, we find that the B3 phase is slightly lower in energy than the B4 phase, and it transforms to B1 structure at 4.19 GPa. Moreover, we found AgI has direct gap in B3 structure with a band gap of 1.378 eV and indirect band gap in B1 phase with a bandgap around 0.710 eV. We also present results of the effective masses for the electrons in the conduction band (CB) and the holes in the valence band (VB). To complete the fundamental characteristics of this compound we have analyzed their linear optical properties such as the dynamic dielectric function and energy loss function for a wide range of 0-25 eV.     

Optoelectronic and thermoelectric properties of Zintl YLi3X2(X=Sb,Bi) compounds through modified Becke—Johnson potential

In the present work, we investigate the structural, optoelectronic and thermoelectric properties of the YLi₃X₂(X=Sb, Bi) compounds using the full potential augmented plane wave plus local orbital (FP-APW+lo) method. The exchange-correlation potential is treated with the generalized gradient approximation/local density approximation (GGA/LDA) and with the modified Becke-Johnson potential (TB-mBJ) in order to improve the electronic band structure calculations. In addition, the estimated ground state properties such as the lattice constants, external parameters, and bulk moduli agree well with the available experimental data. Our band structure calculations with GGA and LDA predict that both compounds have semimetallic behaviors. However, the band structure calculations with the GGA/TB-mBJ approximation indicate that the ground state of the YLi₃Sb₂ compound is semiconducting and has an estimated indirect band gap (Γ-L) of about 0.036 eV while the ground state of YLi₃Bi₂ compound is semimetallic. Conversely the LDA/TB-mBJ calculations indicate that both compounds exhibit semiconducting characters and have an indirect band gap (Γ-L) of about 0.15 eV and 0.081 eV for YLi₃Sb and YLi₃Bi₂ respectively. Additionally, the optical properties reveal strong responses of the herein materials in the energy range between the IR and extreme UV regions. Thermoelectric properties such as thermal conductivity, electrical conductivity, Seebeck coefficient, and thermo power factors are also calculated.     

Coherence and spike death induced by bounded noise and delayed feedback in an excitable system

The first-principles total energy calculations with the generalised gradient approximation and the plane-wave pseudopotential method have been employed to investigate the structural, electronic and dynamical properties of Li₂TiO₃ (lithium titanate). The atomic structure is fully relaxed, and the structural parameters are found to differ by less than 1% from the experimental data. The indirect band-gap with 3.49 eV is predicted from the band structure calculations of this compound. The calculated phonon frequencies at the ??-point for the Raman-active and the infrared-active modes are presented and assigned. The phonon dispersion curves are also calculated along high symmetry lines in the Brillouin zone (BZ). Furthermore, the thermodynamic functions have been worked out using the corresponding phonon density of states, and the results indicate that they are in good agreement with available experimental values.     

Structural stabilities, electronic, elastic and optical properties of SrTe under pressure: A first-principles study

The structural, electronic, elastic and optical properties as well as phase transition under pressure of SrTe have been systematically investigated by first-principles pesudopotential calculations. Five possible phases of SrTe have been considered. Our results show that SrTe undergoes a phase transition from NaCl-type (B1) to CsCl-type (B2) structure at 10.9 GPa with a volume collapse of 9.43%, and no further transition is found. We find that SrTe prefer h-MgO instead of wurtzite (B4) structure for its metastable phase because that the ionic compound prefers a high coordination. The elastic moduli, energy band structures, real and imaginary parts of the dielectric functions have been calculated for all considered phases, and we find that a smaller energy gap yields a larger high-frequency dielectric constant. Our calculated results are discussed and compared with the available experimental and theoretical data.     

Synthesis,spectroscopic properties and DFT study of (E)-1-[(3-(trifluoromethyl)phenylimino)methyl]naphthalen-2-olate

The Schiff base (E)-1-[(3-(trifluoromethyl)phenylimino)methyl]naphthalen-2-olate was synthesized from the reaction of 2-hydroxy-1-naphthaldehyde with 3-trifluoromethylaniline. The title compound has been characterized by FT-IR, UV-vis and X-ray single-crystal techniques. The present X-ray investigation shows that the compound exists in the zwitterionic form. Molecular geometry of the compound in the ground state have been calculated using the density functional method (DFT) with 6-31G(d,p) basis set and compared with the experimental data. The calculated results show that the optimized geometry can well reproduce the crystal structural parameters. By using TD-DFT method electronic absorption spectra of the compound have been predicted and a good agreement with the TD-DFT method and experimental one is determined. In addition DFT calculations of the compound, molecular electrostatic potential (MEP), frontier molecular orbital analysis (HOMO-LUMO) and non-linear optical (NLO) properties were performed at B3LYP/6-31G(d,p).     

宽带隙半导体CdAl_2S_4电子结构、弹性和光学性质的研究

采用基于密度泛函理论(DFT)的第一性原理计算方法,对宽带隙半导体Cd Al_2S_4的晶格结构、电学、弹性和光学性能进行了系统的研究.研究结果表明:Cd Al2S4为直接带隙的宽带隙半导体材料;是弹性稳定的具有各向异性的延展性材料;该晶体的光学性质在中能区(3.5~12.5 e V)具有较强的各向异性,其强反射峰处于紫外能量区域,因此其可用作紫外光探测或屏蔽材料.     

宽带隙半导体CdAl2S4电子结构、弹性和光学性质的研究

采用基于密度泛函理论(DFT)的第一性原理计算方法,对宽带隙半导体CdAl2S4的晶格结构、电学、弹性和光学性能进行了系统的研究. 研究结果表明：CdAl2S4为直接带隙的宽带隙半导体材料;是弹性稳定的具有各向异性的延展性材料;该晶体的光学性质在中能区(3.5 ~12.5 eV)具有较强的各向异性,其强反射峰处于紫外能量区域,因此其可用作紫外光探测或屏蔽材料.     

Study of high pressure behavior and elastic properties of praseodymium monochalcogenides and monopnictides

The structural and elastic properties of praseodymium monochalcogenides (PrX: X = S, Se, Te) and monopnictides (PrY: Y = P, As, Sb, Bi) with NaCl-type structure have been investigated by using an interionic potential theory with necessary modification to include the effect of Coulomb screening due to the delocalized f-electrons of rare earth ion. The calculations are done at ambient as well as at high pressure. The structure of the high pressure phase of PrX compounds is CsCl-type while all the PrY compounds have been found to undergo from their initial NaCl-type structure to high pressure body centered tetragonal (BCT) structure, which can be seen as the distorted CsCl-type with c/a ratio ≈ 0.82–0.87. The calculated transition pressures are in good agreement with the experimental results. The elastic properties like second-order elastic constants for PrX, Y compounds are calculated for the first time. The nature of the bonding is also predicted by calculating the distance between the ions with the increasing pressure.     

First-Principles Study of Structural,Elastic and Electronic Properties of OsSi

First-principles study of structural, elastic, and electronic properties of the B20 structure OsSi has been reported using the plane-wave pseudopotential density functional theory method. The calculated equilibrium lattice and elastic constants are in good agreement with the experimental data and other theoretical results. The dependence of the elastic constants, the aggregate elastic modulus, the deviation from the Cauchy relation, the elastic wavevelocities in different directions and the elastic anisotropy on pressure have been obtained and discussed. This could be the first quantitative theoretical prediction of the elastic properties under high pressure of OsSi compound. Moreover, the electronic structure calculations show that OsSi is a degenerate semiconductor with the gap value of 0.68 eV, which is higher than theexperimental value of 0.26 eV. The analysis of the PDOS reveals that hybridization between Os d and Si p states indicates a certain covalency of the Os-Si bonds.     

Electronic Structure and Optical Properties of the FeAl2 Compound

Physics of the Solid State - The electronic structure and optical properties of the binary intermetallic compound FeAl2 have been studied. Spin-polarized calculations of the electronic structure...     

Structural and magnetic properties of CrSb compounds: NiAs structure

The structural and magnetic properties of CrSb compounds with NiAs structure have been studied by means of the Korringa-Kohn-Rostoker (KKR) band structure method. An analysis of the structural and magnetic stability has been performed on the basis of total energy calculations for various magnetic states. The magnetic properties at finite temperature have been investigated by means of Monte Carlo simulations on the basis of a classical Heisenberg Hamiltonian and the exchange coupling parameters calculated from first principles. This approach allowed us to determine the critical temperature in good agreement with experiment.     

MgS晶体结构性质的密度泛函研究

采用基于密度泛函理论(DFT)基础上的第一性原理赝势平面波方法对MgS晶体四种构型(B1，B2，B3，B4)的体相性质进行了系统研究.计算结果表明，B1构型的晶体是间接带隙型半导体，而B2，B3和B4构型的晶体则是直接带隙型材料，其中B2构型的带隙宽度最窄，其值为0.42eV.在压力不超过200.3GPa时，B1构型的MgS 晶胞是最稳定的，当压力大于该值时，会发生B1构型到B2构型的转化. 关键词： MgS 第一性原理赝势平面波方法 电子结构 转化压力     

Quantum chemical studies of semiconductor surface chemistry using cluster models

Modern quantum chemical methods can be used to investigate many properties of novel molecules and materials with predictive power. We have carried out accurate quantum chemical calculations with cluster models to investigate chemical reactions on semiconductor surfaces. The structure–property relationships that emerge from these studies are illustrated with particular emphasis on silicon as well as indium phosphide surface chemistry. Some new strategies that we have developed to provide a proper balance between covalent and dative bonding in compound semiconductors are discussed. Embedded cluster models have been used in some cases to include the effects of the surroundings on the active region. The structural and mechanistic understanding that emerges from our studies is illustrated by selected results on atomic layer deposition of Al₂O₃ on silicon and hydrogenation of P-rich and In-rich indium phosphide surfaces.     

Structural,elastic and thermodynamic properties of tetragonal and orthorhombic polymorphs of Sr2GeN2: an ab initio investigation

The structural, elastic and thermodynamic properties of the α (tetragonal) and β (orthorhombic) polymorphs of the Sr₂GeN₂ compound have been examined in detail using ab initio density functional theory pseudopotential plane-wave calculations. Apart the structural properties at the ambient conditions, all present reported results are predicted for the first time. The calculated equilibrium lattice parameters and inter-atomic bond-lengths of the considered polymorphs are in good agreement with the available experimental data. It is found that α-Sr₂GeN₂ is energetically more stable than β-Sr₂GeN₂. The two examined polymorphs are very similar in their crystal structures and have almost identical local environments. The single-crystal and polycrystalline elastic parameters and related properties – including elastic constants, bulk, shear and Young’s moduli, Poisson’s ratio, anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature – have been predicted. Temperature and pressure dependence of some macroscopic properties – including the unit-cell volume, bulk modulus, volume thermal expansion coefficient, heat capacity and Debye temperature – have been evaluated using ab initio calculations combined with the quasi-harmonic Debye model.     

Luminescence and structural properties of thermally evaporated benzanthrone dyes thin films

We report optical and luminescence properties of 3-N, N-diacetylaminobenzanthrone thin films deposited on glass substrate by thermal evaporation. The structural and optical properties of organic thin films were studied by means of the confocal microscope with an input of femtosecond laser radiation, X-ray diffractometer, and scanning electron microscope (SEM). Intense luminescence with the maximum at 530 nm was observed when excited by laser radiation with the wavelengths 458, 476, 488, 496, 514 nm. In addition, the luminescence caused by two-photon absorption of femtosecond (fs) laser radiation has been investigated. Semi empirical calculations by AM1 and ZINDO/S methods and ab initio calculations using Gaussian software were carried out to estimate the electron system of structure. The calculations show planar configurations for the aromatic core and diacetylamino fragment of this compound. The study of the structure of benzanthrone derivative thin films with X-ray diffraction (XRD) methods, indicates the distance between molecular layers and ordered molecular fragments.     

The structural, elastic, and electronic properties of the pyrite-type phase for SnO2

We have studied some structural, thermodynamic, elastic, and electronic properties of pyrite-type SnO₂ polymorph by performing ab initio calculations within the LDA approximation. The basic physical properties, in particular lattice constant, bulk modulus, second-order elastic constants (C_ij), and the electronic structure, are calculated, and compared with the available experimental data. In order to gain some further information on the mechanical properties, we have also calculated the Young's modulus, Poison's ratio (ν), anisotropy factor (A), sound velocities, and Debye temperature for the same compound.     

Electronic Structure of the DyFe2Si2 Compound: Energy Band Calculations and Optical Studies

Physics of the Solid State - The electronic structure and the optical properties of the DyFe2Si2 compound have been studied. The calculations of the energy band spectrum taking into account the...     

Prediction study of the structural,elastic, electronic and optical properties of the antiperovskite BiNBa3

We use an ab initio full-potential linear muffin-tin orbital method within the local density approximation (LDA) to study the structural, elastic, electronic and optical properties of the antiperovskite BiNBa₃. The calculated lattice parameter is in good agreement with previous calculations. The elastic constants and their pressure dependence are calculated; we found a linear dependence of elastic stiffness on the pressure. We estimated the Debye temperature of this compound from the average sound velocity. We also present results of the effective masses for the electrons in the conduction band (CB) and the holes in the valence band (VB). To complete the fundamental characteristics of this compound we have analyzed the optical properties.