求解一般约束优化问题的一个全局收敛的混合不精确SQP算法(英文)

对于一般约束优化问题,本文通过一种特殊的耦合策略,把一个局部超线性收敛的不精确SQP算法与广义梯度投影法相结合,从而给出了一个混合算法.该算法无需计算拉格朗日函数的海色矩阵,并且在适当的假设下,算法具有全局和局部超线性收敛性.

Chemical bonding and elastic properties of quaternary arsenide oxides YZnAsO and LaZnAsO investigated by first principles

The structural parameters, chemical bonding and elastic properties of the tetragonal phase quaternary arsenide oxides YZnAsO and LaZnAsO were investigated by using density-functional theory （DFT） within generalized gradient approximation （GGA）. The GGA calculated structural parameters are in agreement with the experimental results. Population analysis suggests that the chemical bonding in YZnAsO and LaZnAsO can be classified as a mixture of ionic and covalent characteristic. Single-crystal elastic constants were calculated and the polycrystalline elastic modules were estimated according to Voigt, Reuss and Hill＇s approximations （VRH）. The result shows that both YZnAsO and LaZnAsO are relatively soft materials exhibiting ductile behavior. The calculated polycrystalline elastic anisotropy result shows that LaZnAsO is more anisotropy in compressibility and YZnAsO is more anisotropy in shear.

Physical Properties of Ⅲ-Antiminodes—a First Principles Study

A comprehensive first principles study of III-Antimonide binary compounds is hardly found in literature. We report a broad study of structural and electronic properties of boron antimonide （BSb）, aluminium antimonide （AlSb）, gallium antimonide （GaSb） and indium antimonide （InSb） in zineblende phase based on density functional theory （DFT）. Our calculations are based on Full-PotentiM Lineaxized Augmented Plane wave plus local orbitals （FP- L（APWq-lo）） method. Different forms of exchange-correlation energy functional and corresponding potential are employed for structural and electronic properties. Our computed results for lattice parameters, bulk moduli, their pressure derivatives, and cohesive energy are consistent with the available experimental data. Boron antimonide is found to be the hardest compound of this group. For band structure calculations, in addition to LDA and GGA, we used GGA-EV, an approximation employed by Engel and Vosko. The band gap results with GGA-EV are of significant improvement over the earlier work.

Electronic Structure Magnetic Properties and Optical Properties of Co-doped AIN from First Principles

The electronic structure, magnetic properties, and optical properties of Co-doped AIN are investigated based upon the Perdew-Burke-Ernzerhof form of generalized gradient approximation within the density functional theory. The band gaps narrowing of AI1-x Cox N are found with the increase of Co concentrations. The analyses of the band structures and density of states show that AI1-xCoxN alloys exhibit a halfometallie character. Moreover, we have succeeded in demonstrating that Co doped AIN system in x = 0.125 is always antiferromagnetie, which is in good agreement with the experimental results. Besides, it is shown that the insertion of Co atom leads to redshift of the optical absorption edge. Finally, the optical constants of pure A1N and AI1-xCoxN alloy, such as loss function, refractive index and reflectivity, are discussed.

Electronic Structure and Optical Properties of Antimony-Doped SnO_2 from First-Principle Study

A first-principles study has been performed to calculate the electronic and optical properties of the SbxSn1xO system.The simulations are based upon the method of generalized gradient approximations with the Perdew-Burke-Ernzerhof form in the framework of density functional theory.The supercell structure shows a trend from expanding to shrinking with the increasing Sb concentration.The increasing Sb concentration induces the band gap narrowing.Optical transition has shifted to the low energy range with increasing Sb concentration.Other important optical constants such as the dielectric function,reflectivity,refractive index,and electron energy loss function for Sb-doped SnO2 are discussed.The optical absorption edge of SnO2 doped with Sb also shows a redshift.

First principles study on electronic structure and optical properties of quaternary arsenide oxides YZnAsO and LaZnAsO

The electronic structure and optical properties of the tetragonal phase quaternary arsenide oxides YZnAsO and LaZnAsO were studied using density-functional theory(DFT) within generalized gradient approximation(GGA).The band structure along the higher symmetry axes in the Brillouin zone,the density of states(DOS) and the partial density of states(PDOS) were presented.The calculated energy band structures show that both YZnAsO and LaZnAsO are indirect gap semiconductors with band gap of 1.173 1 eV and 1.166 5 eV,respectively.The DOS and PDOS show the hybridization of Y-O/La-O atom orbits and Zn-As atom orbits.The dielectric function,reflectivity,absorption coefficient,refractive index,electron energy-loss function and optical conductivity were presented in an energy range from 0 to 25 eV for discussing the optical properties of YZnAsO and LaZnAsO.

First principles study on electronic structure and optical properties of novel Na-hP4 high pressure phase

The electronic structure and optical properties of novel Na-hP4 high pressure phase at different pressures(260,320,400 and 600 GPa)were investigated by the density functional theory(DFT)with the generalized gradient approximation(GGA)for the exchange and correlation energy.The band structure along the higher symmetry axes in the Brillouin zone,the density of states(DOS) and the partial density of states(PDOS)were presented.The band gap increases and the energy band expands to some extent with the pressure increasing.The dielectric function,reflectivity,energy-loss function,optical absorption coefficient,optical conductivity, refractive index and extinction coefficient were calculated for discussing the optical properties of Na-hP4 high pressure phase at different pressures.

First-principles Study of Adsorption and Dissociation of Methanol on the Pt（lO0） Surface

Using first-principles calculations, we studied the interaction of methanol with the Pt（100） surface based on generalized gradient approximation. We found that top sites of Pt（100） surface are the favored adsorptive positions in energy, and methanol molecule interacts with the Pt surface through oxygen atoms. Moreover, we also explored the possible dissociation pathways of methanol on the Pt surface, and suggested that the products of dissociation can be controlled by the external manipulation.

Phase Transition and Phonon Spectrum of Zinc-Blende Structure ZnX (X=S, Se,Te)

Calculations have been performed to investigate the pressure-induced solid-solid phase transitions and the mechanical stability for three zinc-blende II-VI semiconductor compounds： ZnS, ZnSe, ZnTe by ab initio plane-wave pseudopotential density functional theory （DFT）. Using the generalized gradient approximation （GGA） for exchange and correlation in the scheme of Perdew-Wang 1991 （P Wgl ）, the ground state properties and equation of state are obtained, which are well consistent with the experimental data available and other calculations. On the basis of the forth-order Birch-Murnaghan equation of states, the transition pressures Pt are determined through the analysis of enthalpy variation with pressure. A linear-response approach is used to calculate the frequencies of the phonon dispersion. Finally, by the calculations of phonon frequencies, some thermodynamic properties such as the vibrational contribution to the Helmholtz free energy （F）, enthedpy （H）, entropy （S）, and the heat capacity （Cv ） are also successfully obtained.

First-principle investigation on electronic structures and elastic properties of Al-doped MoSi_2

The electronic structures and elastic properties of Al-doped MoSi2 were calculated using the plane wave pseudo-potential method based on the density functional theory,in which the generalized-gradient approximation(GGA) was used to describe the exchange-correlation potential.Starting from the elastic constants,bulk modulus,shear modulus,elastic modulus and Poisson ratio of Al-doped MoSi2 were obtained by using the Hill method.The results indicate that conductivity of Al-doped MoSi2 is improved to some extent in comparison with that of pure MoSi2 due to the orbit hybridization of Mo 4d,Al 3p and Si 3p electrons.In addition,calculations show that the elastic modulus and the brittleness of Al-doped MoSi2 are smaller than those of pure MoSi2,which implies that it is feasible to toughen MoSi2 by doping Al.The agreement of the conclusion with experiment shows that the present theory is reasonable.

Photoabsorption Spectra of Si_n and Si_nO (n ≤ 5)

The photoabsorption spectra have been calculated for Sis and SilO （n ≤ 5） clusters using time-dependent density-function theory. Our studies suggest that Sin-1 O clusters are relatively stable than those of corresponding Sis clusters. Moreover, substantial differences are observed among the absorption spectra of different molecules in the energy region （0 - 8 eV）. Comparing two different exchange-correlation potentials, local-density and generalized-gradient approximations, both calculated optical spectra present the same spectral feature.

First principles calculation on electronic structure,chemical bonding,elastic and optical properties of novel tungsten triboride

The electronic structures,chemical bonding,elastic and optical properties of the novel hP24 phase WB3 were investigated by using density-functional theory(DFT) within generalized gradient approximation(GGA).The calculated energy band structures show that the hP24 phase WB3 is metallic material.The density of state(DOS) and the partial density of state(PDOS) calculations show that the DOS near the Fermi level is mainly from the W 5d and B 2p states.Population analysis suggests that the chemical bonding in hP24-WB3 has predominantly covalent characteristics with mixed covalent-ionic characteristics.Basic physical properties,such as lattice constant,bulk modulus,shear modulus and elastic constants Cij were calculated.The elastic modulus E and Poisson ratio υ were also predicted.The results show that hP24-WB3 phase is mechanically stable and behaves in a brittle manner.Detailed analysis of all optical functions reveals that WB3 is a better dielectric material,and reflectivity spectra show that WB3 can be promised as good coating material in the energy regions of 8.5-11.4 eV and 14.5-15.5 eV.

Magnetism and Sound Velocities of Iron Carbide （Fe3C） under Pressure

The elastic property and sound velocity of FeaC under high pressure are investigated by using the spin-polarized generalized gradient approximation within density-functional theory. It is found that the magnetic phase transition from the ground ferromagnetic （FM） state to the nonmagnetic （NM） state occurs at ～73 GPa. Based on the predicted Hugoniot of Fe3C, we calculate the sound velocities of FM-Fe3C and NM-Fe3C from elastic constants. Compared with pure iron, NM-FeaC provides a better match of compressional and shear sound velocities with the seismic data of the inner core, supporting carbon as one of the light elements in the inner core.

Combined Gradient Representations for Generalized Birkhoffian Systems in Event Space and Its Stability Analysis

The combined gradient representations for generalized Birkhoffian systems in event space are studied.Firstly,the definitions of six kinds of combined gradient systems and corresponding differential equations are given.Secondly,the conditions under which generalized Birkhoffian systems become combined gradient systems are obtained. Finally,the characteristics of combined gradient systems are used to study the stability of generalized Birkhoffian systems in event space. Seven examples are given to illustrate the results.

A first-principles study of the structural,electronic and elastic properties of solid nitromethane under pressure

The structural,electronic and elastic properties of solid nitromethane are investigated under pressure by performing first-principles density functional theory(DFT)calculations within the generalized gradient approximation(GGA)and the local density approximation(LDA).The obtained ground state structure properties are found to be consistent with existing experimental and theoretical results.The pressure-induced variations of structure parameters(a,b,c and V)indicate that the solid nitromethane has an anisotropic compressibility,and the compression along the c direction is more difficult than along a and b directions.From the vibration curves of intermolecular bond length and bond angle,we find that the C—N bond is the most sensitive among these bonds under pressure,suggesting that the C—N bonds may be broken first under external loading.The influence of pressure on the electronic properties of solid NM has been studied,indicating that solid NM is an insulating compound with a large indirect band gap and tends to be a semiconductor with increasing pressure.Finally,we predict the elastic constants and their pressure dependence for the solid NM with the bulk modulus,Young’s modulus,shear modulus and the Poisson’s ratio derived.

First-principles investigation of the effects of B impurities on the mechanical properties of NiAl intermetallics

We have investigated the effects of B impurities on the structure and mechanical properties of NiA1 intermetallics by using a first-principles pseudopotential total-energy method, based on the density functional theory with a generalized gradient approximation. We found that the impurity B atoms can either replace Ni atoms or Al atoms or both, depending on the surround- ing environment. We demonstrated that the presence of B will cause an increase in brittleness and a decrease in the ductility of NiAI for the Al-substitutional case, while causing an increase in the ductility of NiAl for the Ni-subtitutional case, based on the calculated elastic constants and the empirical criterions. This indicates that the effects of B impurities on the mechanical prop- erties of NiAl intermetallics are quite composition-dependent.

Hydrostatic pressure influence on magnetic phase diagram and structural parameters of SrTcO_3 from first-principles calculations

The effects of hydrostatic pressure of SrWeO3 are investigated by means of generalized gradient approximation （GGA） plus on-site Coulomb interaction corrections （GGA＋U） method within the framework of density functional theory （DFT）. Magnetic phase diagrams and structural parameters of SrTcO3 as a function of pressure are predicted. The magnetic ground state of SrTcO3 is found to keep in a G-type antiferromagnetic （G-AFM） structure under the pressure varying from 0 to 100 GPa. With the increase of the pressure, magnetic exchange energy increases, indicating a higher magnetic ordering temperature for SrTcO3 under a larger pressure. Besides the volume of the unit cell, lattice constants, and the bond length, the angles between typical Tc-O-Tc and Sr-O-Sr also decrease with the pressure, leading to strong structural distortions. Very obvious displace- ments of Sr and O atoms are observed under the pressure. Our work provides necessary understanding on electronic structures of SrTcO3 under high pressures.

Mechanical Anisotropic and Electronic Properties of Amm2-carbon under Pressure

Structural, electronic properties and mechanical anisotropy of Amm2-carbon are investigated utilizing tlrst-principles calculations by Oambridge Serial Total Energy Package （CASTEP） code. The work is performed with the generalized gradient approximation in the form of Perdew Burke-Ernzerhof （PBE）, PBEsol, Wu and Cohen （WC） and local density approximation in the form of Ceperley and Alder data as parameterized by Perdew and Zunger （CA-PZ）. The mechanical anisotropy eMculations show that Amm2-carbon exhibit large anisotropy in elastic moduli, such as Poisson＇s ratio, shear modulus and Young＇s modulus, and other anisotropy factors, such as the shear anisotropic factor and the universal anisotropic index AU. It is interestingly that the anisotropy in shear modulus and Young＇s modulus, universal anisotropic index and the shear anisotropie factor all increases with increasing pressure, but the anisotropy in Poisson＇s ratio decreases. The band structure calculations reveal that Amm2-carbon is a direct-band-gap semiconductor at ambient pressure, but with the pressure increasing, it becomes an indirect-band-gap semiconductor.

Generalized Green Correspondence of Graded Modules

The author studies the Green correspondence and quasi-Green correspondence for indecomposable modules over strongly graded rings. The motivation is to investigate the influence of induction and restriction processes on indecomposability of graded modules.