First-principles calculations of structural, electronic, and thermodynamic properties of ZnO_(1-x)S_x alloys

In this study the pseudo-potential method is used to investigate the structural, electronic, and thermodynamic proper- ties of ZnOl_xSx semiconductor materials. The results show that the electronic properties are found to be improved when calculated by using LDA ~ U functional as compared with local density approximation （LDA）. At various concentrations the ground-state properties are determined for bulk materials ZnO, ZnS, and their tertiary alloys in cubic zinc-blende phase. From the results, a minor difference is observed between the lattice parameters from Vegard＇s law and other calculated results, which may be due to the large mismatch between lattice parameters of binary compounds ZnO and ZnS. A small deviation in the bulk modulus from linear concentration dependence is also observed for each of these alloys. The ther- modynamic properties, including the phonon contribution to Helmholtz free energy △F, phonon contribution to internal energy △E, and specific iheat at constant-volume Cv, are calculated within quasi-harmonic approximation based on the calculated phonon dispersion relations.

Theoretical calculations of structural, electronic, and elastic properties of CdSe_(1-x)Te_x:A first principles study

The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of Cd Se_（1-x）Te_x in the zinc blende phase. It is observed that the electronic properties are improved considerably by using LDA ＋ U as compared to the LDA approach. The calculated lattice constants and bulk moduli are also comparable to the experimental results. The cohesive energies for pure Cd Se and Cd Te binary and their mixed alloys are calculated. The second-order elastic constants are also calculated by the Lagrangian theory of elasticity. The elastic properties show that the studied material has a ductile nature.

Forward Calculation of 2-D and 3-D Structures with a Cover by the Boundary Element Method while Using Electrical Methods

This paper develops the boundary element method, the authors employ two-layered earth Green 's functions as the weighting functions of residual and derive boundary integral equations. The forward problems of point sources on 2 - D and 3-D structures with an influencing cover are solved by this method. The results show that this method markedly improves the original boundary element method. The features of the improved method are greater numerical accuracy and much smaller systems of equations and thus considerable savings for the storage capacity of computers, allowing us to solve the above problems with only ordinary microcomputers. The results in this paper extend the scope of applying the boundary element method while using electrical methods for geophysical prospecting.

Enhanced Property of Thin Cuprous Oxide Film Prepared through Green Synthetic Route

Thin cuprous oxide films have been prepared by chemical vapor deposition(pulsed spray evaporation-chemical vapor deposition)method without post-treatment.The synthesis of cuprous oxide was produced by applying a water strategy effect.Then,the effect of water on the morphology,topology,structure,optical properties and surface composition of the obtained films has been comprehensively investigated.The results reveal that a pure phase of Cu2O was obtained.The introduction of a small quantity of water in the liquid feedstock lowers the band gap energy from 2.16 eV to 2.04 eV.This finding was mainly related to the decrease of crystallite size due to the effect of water.The topology analyses,by using atomic force microscope,also revealed that surface roughness decreases with water addition,namely more uniform covered surface.Moreover,theoretical calculations based on density functional theory method were performed to understand the adsorption and reaction behaviors of water and ethanol on the Cu2O thin film surface.Formation mechanism of the Cu2O thin film was also suggested and discussed.

NONLINEAR EVOLUTION SYSTEMS AND GREEN’S FUNCTION

In this paper, we will introduce how to apply Green＇s function method to get the pointwise estimates for the solutions of Cauchy problem of nonlinear evolution equations with dissipative structure. First of all, we introduce the pointwise estimates of the time-asymptotic shape of the solutions of the isentropic Navier-Stokes equations and show to exhibit the generalized Huygen＇s principle. Then, for other nonlinear dissipative evolution equations, we will only introduce the result and give some brief explanations. Our approach is based on the detailed analysis of the Green＇s function of the linearized system and micro-local analysis, such as frequency decomposition and so on.

Theoretical investigation of sulfur defects on structural, electronic,and elastic properties of ZnSe semiconductor

The structural, electronic, and elastic properties of ZnSe1-xSx for the zinc blende structures have been studied by using the density functional theory. The calculations were performed using the plane wave pseudopotential method, as implemented in Quantum ESPRESSO. The exchange-correlation potential is treated with the local density approximation pz-LDA for these properties. Moreover, LDA＋U approximation is employed to treat the ＂d＂ orbital electrons properly. A comparative study of the band gap calculated within both LDA and LDA＋U schemes is presented. The analysis of results show considerable improvement in the calculation of band gap. The inclusion of compositional disorder increases the values of all elastic constants. In this study, it is found that elastic constants C11, C12, and C44 are mainly influenced by the compositional disorder. The obtained results are in good agreement with literature.

Density Functional Theory for Battery Materials

Batteries are the most widely used energy storage devices, and the lithiumion battery is the most heavily commercialized and most widely used battery type in the industry. However, the current rapid development of society requires a major advancement in battery materials to achieve high capacity,long life cycle, low cost, and reliable safety. Therefore, many new efficient energy storage materials and battery systems are being developed and explored, and their working mechanisms must be clearly understood before industrial application. In recent years, density functional theory (DFT) has been employed in the energy storage field and has made significant contributions to the understanding of electrochemical reaction mechanisms and to virtual screening of promising energy storage materials. In this review,the applications of DFT to battery materials are summarized and exemplified by some representative and up-to-date studies in the literature. The main focuses in this review include the following:1) structural stability estimation by cohesive energy, formation energy, Gibbs free energy, and phonon dispersion spectra calculations;2) the Gibbs free energy calculations for electrochemical reactions, corresponding open-circuit voltage, and theoretical capacity predictions of batteries;3) the analyses of molecule orbitals, band structures, density of states (DOS), and charge distribution of battery materials;4) ion transport kinetics in battery materials;5) simulations of adsorption processes. We conclude the review with the discussion of the assessments and validation of the popular functionals against several benchmarks, and a few suggestions have been given for the selection of density functionals for battery material systems.

约束Green函数与非线性地基梁模态分析

在生物和医学领域,微机电系统(MEMS)中的微梁结构在植入人体的使用时,由于体内的细胞环境类似于水凝胶,在这种环境下工作,设备和仪器的精度和稳定性很大程度上受到细胞弹性的影响.为了分析此类地基梁的动力学问题,本文建立了非线性基础上的梁振动模型,研究了任意位置弹簧和非线性弹簧基础上的梁模态.通过Laplace变换和线性叠加原理,得到了一种约束Green函数,利用数值计算验证方案的有效性,并研究了各种重要物理参数的影响,发现弹簧位置向跨中移动时,模态对称性被打破,弹簧刚度增加,模态阶数改变.

An easy and efficient way to treat Green's function for nano-devices with arbitrary shapes and multi-terminal configurations

The efficiency of the calculation of Green＇s function （GF） for nano-devices is very important because the calculation is often needed to be repeated countlessly. We present a set of efficient algorithms for the numerical calculation of GF for devices with arbitrary shapes and multi-terminal configurations. These algorithms can be used to calculate the specified blocks related to the transmission, the diagonals needed by the local density of states calculation, and the full matrix of GF, to meet different calculation levels. In addition, the algorithms for the non-equilibrium occupation and current flow are also given. All these algorithms are described using the basic theory of GF, based on a new partition strategy of the computational area. We apply these algorithms to the tight-binding graphene lattice to manifest their stability and efficiency. We also discuss the physics of the calculation results.

First-principles investigation of chemical modification on two-dimensional iron-phthalocyanine sheet

Successful synthesis of single iron-phthalocyanie （FePc） framework layer on substrate and its transferrable properties open the door for decorating the separately distributed transition metals for exploring the diverse properties. We have studied the effects of chemical modification on two-dimensional FePc organometallic framework with density functional theory. For simplicity, the non-metal atoms with variant valence electrons are used as prototypes to estimate the effects ＆ore chemical modifications with different functional groups. The thermo-stabilities of the non-metal atom decorated complex sheet materials have been estimated by the first-principles constant energy molecular dynamic simulations. Upon the non- metal atom adsorption, the magnetic moment could be changed from 2 ~tB to 0, 1, 2, and 3 ~tB per unit cell for the case of tetra-, penta-, hexa-, and hepta-valent non-metal modifications, respectively, showing interesting promise to tailor its magnetic properties for potential applications.

饱和土中伴有排水问题爆炸场动力反应Green函数计算

饱和土在动力作用下伴有排水的反应是工程中常见的现象,其计算也是一个非常复杂的数学力学问题。根据已经求得的集中力作用下两相饱和介质Green函数基本解,得到球坐标的扩张源固相位移时域Green函数的表达式。再以物理的方法推导出球坐标中心扩张源时域流相的压力Green函数;以及相对应的注入流相后,场点的时域固相位移Green函数和流相压力Green函数的表达式。再结合导出的两相饱和介质Lamb方程,进行动力排水问题的计算,解决饱和土爆炸场中伴有排水的动力反应计算问题。

层土动力Green函数数值计算中若干问题的探讨

动力Ｇｒｅｅｎ函数数值计算技术是动力边界元法得以实施的关键技术之一。本文首先对两类层状介质动力Ｇｒｅｅｎ函数的频域解进行了比较。在此基础上，文中着重探讨了在土一结构相互作用问题中应用显式动力Ｇｒｅｅｎ函数时的著于数值计算问题，包括土层的子层离散和波数的计算以及半空间的模拟等。最后给出了这一动力Ｇｒｅｅｎ函数在处理层状半无限空间问题时的合理方法。

Structures, stabilities and magnetic moment of small copper-nickel clusters

This paper obtains the lowest-energy geometric structures and the electronic and magnetic properties of small CuNiN clusters by using all-electron density functional theory. The calculated results reveal that the Cu atom prefers to occupy the apical site when N ≤ 9 and for the clusters with N = 10, the Cu atom starts to encapsulate in the cage. The CuNi7 and CuNi9 are magic clusters. The magnetism correlates closely with the symmetry of the clusters. For these clusters, the charge tends to transfer from the nickel atoms to the copper atoms. It finds that the doping of Cu atom decreases the stability of pure NiN clusters.

THE POINTWISE ESTIMATES TO SOLUTIONS FOR 1-DIMENSIONAL LINEAR THERMO-VISCO-ELASTIC SYSTEM

In this paper, we study the linear thermo-visco-elastic system in one-dimensional space variable. The mathematical model is a hyperbolic-parabolic partial differential system. The solutions of the system show some decay property due to the parabolicity. Based on detailed analysis on the Green function of the system, the pointwise estimates of the solutions are obtained, from which the generalized Huygens’ principle is shown.

Green's function calculations of light nuclei

The influence of short-range correlations in nuclei was investigated with realistic nuclear force. The nucleon-nucleon interaction was renormalized with Vlowk technique and applied to the Green's function calculations. The Dyson equation was reformulated with algebraic diagrammatic constructions. We also analyzed the binding energy of 4He, calculated with chiral potential and CD-Bonn potential. The properties of Green's function with realistic nuclear forces are also discussed.

First-principle study of geometries, electronic structures and vibrational spectra of neutral and anionic onion-like [As@Ni12@As20]

We present results of first-principle study for both neutral and anionic onion-like [As@Ni12@As20]. The groundstates of singly-charged and doubly-charged anions deviate from ideal Ih symmetrical geometry because of Jahn-Teller effect, whereas the triply-charged singlet and neutral quartet have similar stable geometries of Ih symmetry. The infrared and Raman spectra may provide a way to determine various charge states of this molecule with the same symmetry. Based on our systematical calculations, we suggest additional experimental measurements in order to determine the appropriate functional with great confidence, which should be important in the research for future quantum dot devices.

常微分方程中的齐次化原理与Green函数

通过介绍齐次线性微分方程的通解及求非齐次微分方程的特解的一种方法,定义了Green函数.

杂多酸型离子液体杂化材料的第一性原理研究

构建了三种同系杂多酸型离子液体模型,随后用密度泛函理论分析并讨论了它们微观结构、结合能、载流子有效质量.结果表明杂多酸的取代配位原子数目会对杂化物的性质产生较大影响.在钼取代的磷钨酸中,当钼取代数目低时,杂化物载流子有效质量较低,呈较强的导电性.高钼取代数时载流子的相对质量较大,因此传输阻力增大,其导电性于低钼取代数目的杂化物.以此对所合成材料的性质进行预测与验证,为以后合成、分析这类物质提供理论依据和指导作用.

反应堆合金材料腐蚀的密度泛函理论计算研究现状

经过几十年的研究,对现有反应堆合金材料服役工况下的腐蚀问题及规律已经有了较为清晰的认识,但是依然存在一些待解决的问题,如对反应堆合金材料腐蚀中本质过程的理解,单一因素在腐蚀过程中所起的作用,新材料以及极端环境下的腐蚀行为预测等。基于量子力学的密度泛函理论(Density Functional Theory,DFT)计算可以精确地预测极短时间内原子的运动过程以及相关能量的变化,近年来逐渐成为反应堆合金材料腐蚀过程研究的重要辅助手段,这将有助于解决上述问题。本文首先介绍了DFT方法,主要包括理论基础、发展过程与主流计算软件。然后对DFT理论在反应堆合金材料腐蚀领域应用的研究现状进行了综合论述和分析,包括水冷堆、液态金属冷却堆、熔盐堆介质环境中反应堆合金材料表面的吸附、解离、结合、内部扩散等腐蚀行为。最后展望了DFT应用在反应堆合金材料腐蚀方面的未来发展趋势。

深度学习与第一性原理计算

第一性原理计算基于量子力学基本原理,通过求解复杂的多电子相互作用问题实现高精度材料计算预测,已成为现代物理学、化学、材料科学等诸多领域中不可或缺的研究手段。然而,高昂的计算成本限制了第一性原理计算的广泛应用,使得大尺度材料模拟和材料大数据构建等重要领域的发展面临重大挑战。近年来,Alpha Go、Alpha Fold、Chat GPT等突破性工作的涌现宣示了人工智能新时代的来临,第一性原理计算领域也迎来了变革性转变的历史机遇。深度学习为第一性原理计算提供了新的研究范式,通过精确建模和高效预测,有望突破传统方法的瓶颈问题。文章介绍了一类基于深度学习的第一性原理计算方法,利用神经网络对密度泛函理论中的核心物理量——密度泛函理论哈密顿量进行建模,并设计出满足局域性原理、协变性原理等关键物理先验的先进神经网络架构,实现了高效精确的深度学习电子结构计算。该方法已成功应用于转角范德瓦耳斯材料等体系的大尺度材料模拟、基于材料大数据的通用材料模型构建等极具挑战性的任务中,为发展材料大模型、推动人工智能驱动的材料发现提供了新的机遇。