Valence band structure and density of states effective mass model of biaxial tensile strained silicon based on k·p theory

After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k·p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states （DOS） effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal-oxide semiconductor field effect transistor （MOSFET）. It also a provides valuable reference for biaxial tensile strained silicon MOSFET design.

Ab-initio density functional theory study of a WO_3 NH_3-sensing mechanism

WO3 bulk and various surfaces are studied by an ab-initio density functional theory technique. The band structures and electronic density states of WO3 bulk are investigated. The surface energies of different WO3 surfaces are compared and then the （002） surface with minimum energy is computed for its NH3 sensing mechanism which explains the results in the experiments. Three adsorption sites are considered. According to the comparisons of the energy and the charge change between before and after adsorption in the optimal adsorption site Olc, the NH3 sensing mechanism is obtained.

Density functional theory calculations of tetracene on low index surfaces of copper crystal

This paper carries out the density functional theory calculations to study the adsorbate-substrate interaction between tetracene and Cu substrates （Cu （110） and Cu （100） surface）. On each of the surfaces, two kinds of geometry are calculated, namely ＇flat-lying＇ mode and ＇upright standing＇ mode. For ＇flat-lying＇ geometry, the molecule is found to be aligned with its longer molecular axis along close-packed direction of the substrate surfaces. For ＇upright standing＇ geometry, the long axis of tetracene is found to be parallel to the surface normal of the substrate on Cu （110） surface. However, tetracene appears as ＇tilted＇ mode on Cu （100） surface. Structures with ＇flat-lying＇ mode have much larger adsorption energy and charge transfer upon adsorption than that with ＇upright standing＇ mode, indicating the preference of ＇flat-lying＇ geometry on both Cu （110） and Cu （100） surface.

Determination of Band Structure of Gallium-Arsenide and Aluminium-Arsenide Using Density Functional Theory

This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].

Correlation of the mean activity coefficient of aqueous electrolyte solutions using an equation of state

Accurate calculation of thermodynamic properties of electrolyte solution is essential in the design and optimization of many processes in chemical industries. A new electrolyte equation of state is developed for aqueous electrolyte solutions. The Carnahan-Starling repulsive model and an attractive term based on square-well potential are adopted to represent the short range interaction of ionic and molecular species in the new electrolyte EOS. The long range interaction of ionic species is expressed by a simplified version of Mean Spherical Approximation theory （MSA）. The new equation of state also contains a Born term for charging free energy of ions. Three adjustable parameters of new eEOS per each electrolyte solution are size parameter, square-well potential depth and square-well potential interaction range. The new eEOS is applied for correlation of mean activity coefficient and prediction of osmotic coefficient of various strong aqueous electrolyte solutions at 25℃ and 0.1 MPa. In addition, the extension of the new eEOS for correlation of mean activity coefficient and solution density of a few aqueous electrolytes at temperature range of 0 to 100℃ is carried out.

Orbital Calculations of Kaolinite Surface:on Substitution of Al^(3+) for Si^(4+) in the Tetrahedral Sites

The surface properties of kaolinite were determined using density functional theory discrete variational method （DFT-DVM） and Gaussian 03 program. A SiO4 tetrahedral hexagonal ring with two A1 octahedra was chosen to model the kaolinite crystal. The total density of states of the kaolinite cluster are located near the Fermi level at both sides of the Fermi level. Both the highest occupied molecular orbit （HOMO） and the lowest unoccupied molecular orbit （LUMO） of kaolinite indicate that kaolinite system can not only readily interact with electron-acceptor species, but also readily interact with electron-donor species on the edge surface and the gibbsite layer surface, and thus, shows amphoteric behavior. Substitution of Al3^＋ for Si4＋ in the tetrahedral site linking the vacant Al3^＋ octahedra does not increase the surface chemical reactivity of kaolinite, while substitution of Al3^＋ for Si^4＋ in the tetrahedral site with the apex O linking Al3^＋ octahedra increase the surface chemical reactivity of the siloxane surface of kaolinite, especially acting as electron donors. Additionally, substitution of Al3^＋. for Si^4＋ in the tetrahedral site results in the re-balance of charges, leading to the increase of negative charge of the coordinated O atoms of the AlO4 tetrahedra, and therefore favoring the formation of ionic bonds between cations and the surface O atoms in the basal plane.

ELECTRONIC STRUCTURES OF (CdSe)_n/(ZnSe)_m STRAINED-LAYER SUPERLATTICES

The electronic structures of (CdSe)n/(ZnSe)m strained-lager soperfattice (SLS) were investigated by the recursion method in the tight-bindiop opproximation. The total,local, and partial density of states were calculated for n=1, m=5.The total density of states (TDOS) for bulk CdSe, ZnSe and n=1, 3, m=1, 3, 5, for SLS were investigated.Fermi energy, the band gap, the valence of an atom, and the ionization potential and the electron affinity were discassed.

Molecular dynamics simulations of strain-dependent thermal conductivity of single-layer black phosphorus

Classical molecular dynamics(MD)simulations ae performed to investigate the effects of mechanical strain on the thermal conductivity of single-layer black phosphorus(SLBP)nanoribbons along different directions at room temperature.The results show that the tensile strain afects the thermal conductivity of nanoribbons by changing thephonon density of state(DOS)and mean free path(M FP).The thermal conductivity shows a sharp enhancement with the tensile strain applied along the armchai diection,while it increases slowly with the strain applied along the zigzag diection.This phenomenon cm be mainly explained by effects of the phonon DOS and MFP.The increasing strain along the armchai direction weakens DOS and strengthens MFP clearly.However,when it comes to the increasing strain along the zigzag deection'DOS enliances significantly while MFP decreases slightly.The findings explore the relationship between the tensile strain and the thermal conductivity reasonably and can provide a reliable method to estimate the MFP of black phosphorus.

Size effect of quantum conductance in carbon nanotube Y-Junctions

This paper studies the quantum conductance properties of three-terminated carbon nanotube Y-junctions, which are built by connecting three （5,5） single-walled carbon nanotubes. The results show that the quantum conductance at the Fermi energy oscillates periodically with the junction＇s size, and the number of oscillating periodic layers is 3 which is the same as that in the two terminated （10, 0）/m（5, 5）/（10, 0） junctions. Moreover, this Y-junction with different size exhibits an obviously different distribution of electron current in the two drain branches, called shunt valve effect of electronic current. Thus the degree of this effect can be controlled and modulated directly by constructing the three branches＇ sizes or the distribution of defect. The results show in detail that the difference between the two drain currents can be up to two times for some constructions with special sizes. In addition, the uniform distribution of defects in the Y-junction leads to lower quantum conductance than that of other defect configurations.

O2, CO2, and H2O Chemisorption on UN（001） Surface： Density Functional Theory Study

We performed density functional theory calculations of O2, CO2, and H2O chemisorption on the UN（001） surface using the generalized gradient approximation and PW91 exchangecorrelation functional at non-spin polarized level with the periodic slab model. Chemisorption energies vs. molecular distance from UN（001） surface were optimized for four symmetrical chemisorption sites. The results showed that the bridge parallel, hollow parallel and bridge hydrogen-up adsorption sites were the most stable site for O2, CO2, and H2O molecular with chemisorption energies of 14.48, 4.492, and 5.85 kJ/mol, respectively. From the point of adsorbent （the UN（001） surface）, interaction of O2 with the UN（001） surface was of the maximum magnitude, then CO2 and H2O, indicating that these interactions were associated with structures of the adsorbate. O2 chemisorption caused N atoms on the surface to migrate into the bulk, however CO2 and H2O had a moderate and negligible effect on the surface, respectively. Calculated electronic density of states demonstrated the electronic charge transfer between s, p orbital in chemisorption molecular and U6d, U5f orbital.

First-principles Study on the Electronic Structure and Stability of Mo_(2-x)Cr_xC

This paper deals with the electronic structure and stability of a series of carbides Mo2-xCrxC based on the pseudopotential plane-waves approach of density functional theory and using the generalized gradient approximation(GGA) for the exchange and correlation potential.The calculation results of formation energies demonstrate that the structure Mo2-xCrxC in range of 0≤x≤1.75 is stable under ambient conditions.The formation energies/stabilities of the structures Mo2-xCrxC increase /reduce with enhancing the content of Cr in the structure.Calculated density of state(DOS) show that an increase in the content of Cr dissolving in Mo2-xCrxC crystal cell can lead to the crystal cell volume slightly to shrinkage,TDOS to be elevated at the Fermi level and the peak value of DOS to decrease at the lower energy region from-13.78 to-10.16 eV.Mulliken population analysis explains that the Mo2-xCrxC phase possess the metallic,covalent and ionic bonds.

Study of Electronic Structure and Magnetic,Properties of NdFe_(10)M_2 Compounds by LMTO Method

The electronic structure of NdFe 10 M 2(M=Ti, V, Cr, Mn, Mo, W) compounds were obtained by the linear muffin tin orbit(LMTO) method, and the micro magnetic properties were examined through the total density of state(TDOS) and the local density of state(DOS). The results suggest that there are two mechanisms which compete with each other and are responsible for variations in magnetic moments of NdFe 10 M 2 with intertitial N(or C) atoms, and the volume expansion leads to the enhancement of Fe Fe exchange interaction at 8i and 8f site, with the result that the magnetic moments at both sites increase. Meanwhile, the magnetic moments at 8j site decrease owing to the hybridization between 3d(Fe) and 2p(N or C) orbits.

Intrinsic Carrier Concentration as a Function of Stress in(001),(101) and(111) BiaxiallyStrained-Si and Strained-Si_(1-x)Ge_x

Intrinsic carrier concentration(ni) is one of the most important physical parameters for understanding the physics of strained Si and Si1-xGex materials as well as for evaluating the electrical properties of Si-based strained devices. Up to now, the report on quantitative results of intrinsic carrier concentration in strained Si and Si1-xGex materials has been still lacking. In this paper, by analyzing the band structure of strained Si and Si1-xGex materials, both the effective densities of the state near the top of valence band and the bottom of conduction band( Nc and Nv) at 218, 330 and 393 K and the intrinsic carrier concentration related to Ge fraction(x) at 300 K were systematically studied within the framework of KP theory and semiconductor physics. It is found that the intrinsic carrier concentration in strained Si(001) and Si1-xGex(001) and(101) materials at 300 K increases significantly with increasing Ge fraction(x), which provides valuable references to understand the Sibased strained device physics and design.

Evidence for Non-existence of Oscillations in Photofield Emission Current in Gallium Arsenide

We have shown here the results of PFEC(photofield emission current)calculated for GaAs(gallium arsenide).We have used the initial state wavefunctions derived using the Kronig-Penney potential model for evaluating the PFEC.We have found that PFEC is not oscillatory as obtained by Modinos and Klient,[Solid State Commun.50,651(1984)],but it is an exponential function.

The influence of cation additives on the NIR luminescence intensity of Er^(3+)-doped borate glasses

Er3+-doped 25BaO-(25-x)SiO2-xAl2O3-25B2O3 transparent glasses are prepared with x = 0,12.5 and 25 by a solid-state reaction.The Er-related NIR luminescence intensity,which corresponds to the transition of 4I15/2-4I13/2,is obviously altered with different silicon/aluminum ratios.The Judd-Ofelt parameters of the Er3+ ions are adopted to explain the intensity change in the NIR fluorescence,and the Raman scattering intensity versus the amount of Al and/or Si components are discussed.The spectra of the three samples are quite similar in the peak positions,but different in intensity.The maximal phonon density of state for the samples is calculated from the Raman spectra and is correlated to the NIR luminescence efficiency.

Se AND Bi SUBSTITUTION EFFECT IN Sb_2Te_3

The Discrete Variational Xα Method DV-Xα with an embeded cluster scheme was used to investigate electronic structure, energy levels, charge distribution and chemical bonding in p-type thermoelectric ceramics :Sb2Te3-Bi2Te3-Sb2Se3. The results obtained are in agreement with experiment ones, which are instructive to material design.

A Polymeric Iodiplumbate(Ⅱ) Templated by Conjugated Quaternary Ammonium:Synthesis,Band Structure and Optical Properties

A new lead（Ⅱ） iodide coordination polymer [（npq）（PbI3）]n1 （npq = N-propyl- quinolinium） has been synthesized in the presence of npq as structure-directing reagent （SDA）. Compound 1 crystallizes in the orthorhombic system, space group Pbca, with a = 19.158（4）, b = 7.9909（16）, c = 22.929（5） A, V = 3510.2（12） A3, Z = 8, Dc = 2.877 g/cm3, F（000） = 2672, C12H1413NPb, Mr= 760.14, μ（MoKα） = 14.872 mm-1, the final R = 0.0431 and wR = 0.1021 for 3678 observed reflections with Ⅰ 〉 2σ（Ⅰ）. Structure determination indicates that the [PbI3]^-n infinite chains in each unit cell shape the sketch of 1, which could be described as the result of face-sharing distorted PbI6 octahedra running along the b axis. Electrostatic interaction between conjugated organic counter-cations and inorganic moieties presents and contributes to the crystal packing. 1 was further characterized with IR and elemental analysis. Based on the crystal structure data, quantum chemical calculation with DFT method was used to reveal the electronic structure and optical property of 1.

A density functional study on the electronic structures of TiN solid

The electronic structures of TIN bulk have been studied by using different theoretical formalisms, and the DFT method, especially the BLYP method can produce reasonable results. The band structure of TIN(00l) surface is also investigated and two σ type surface states are presented in our results. The state located at 2.9 eV below EF in angle resolved photoemission in (ARPES) is well reproduced in this work, which consists essentially of 2pz orbital of surface N atom. Another surface state is associated with the bands originated from 3d orbital of surface Ti atom. Furthermore, the elastic constants of TiN are also calculated by using BLYP method.

Ab initio Study of Electronic Structure and Properties of Crystalline of 1,5-Diamino-1,2,3,4-tetrazole

Density functional method was applied to study 1,5-diamino-1,2,3,4-tetrazole （DAT, CH4N6） in both gaseous and bulk states. The banding and electronic structures of crystalline have been investigated at DFT-B3LYP/ 6-311G＊＊ level of theory. Relaxed crystal structure compares well with experimental data. The light fluctuation of the frontier orbital, which is mainly formed by atomic orbital of N（4） （heterocycle）, is the most reactive part of the molecule, which is in good agreement with the experimental results. The energy gap is 9.035 eV, which indicates that DAT is an insulator. The distribution of electrostatic potential is uniform, indicating DAT is insensitive. The charge density of the intermolecular regions in the plane is not overlaid, indicating that the intermolecular interac- tion between the neighboring molecules along this direction in the bulk is very weak. The overlap populations of N（1）--N（2） bonds are much less than those of other bonds, therefore the N（1）--N（2） bonds first rupture by external stimuli.

Predictions of high-pressure structural, electronic and thermodynamic properties of α-Si_3N_4

The plane-wave pseudo-potential method within the framework of first-principles technique is used to investigate the fundamental structural properties of Si3N4. The calculated ground-state parameters agree quite well with the experimental data. Our calculation reveals that α-Si3N4 can retain its stability to at least 45 GPa when compressed below 300 K. No phase transition can be seen in the pressure range of 0-45 GPa and the temperature range of 0-300 K. Actually, the α→β transition occurs at 1600 K and 7.98 GPa. Many thermodynamic properties, such as bulk modulus, heat capacity, thermal expansion, Gr/ineisen parameter and Debye temperature of a-Si3N4 were determined at various temperatures and pressures. Significant differ- ences in these properties were observed at high temperature and high pressure. The calculated results are in good agreement with the available experimental data and previous theoretical values. Therefore, our results may provide useful information for theoretical and experimental investigations of the N-based hard materials like α-Si3N4.