23MnNiMoCr54钢中温回火组织电子结构参数及强度计算

利用固体与分子经验电子理论(EET),分析了矿用圆环链23MnNiMoCr54钢中温回火组织特征相,并计算了特征相及相面电子结构参数n'A、△ρ'、σN和σ,最后利用电子结构参数计算了23MnNiMoCr54钢中温回火后的抗拉强度,计算结果与实际符合较好.     

氧化钒晶体的半导体至金属相变的理论研究

本文利用第一性原理方法研究了金红石相和单斜相VO₂晶体的电子结构和热力学性质.在计算中采用局域密度近似结合Hubbard U模型(LDA+U)描述电子的局域强关联效应,同时也利用微扰密度泛函方法计算了两种相结构的声子谱.计算结果表明V原子3d电子轨道中x²-y²轨道能级分裂决定了VO₂晶体在不同相结构下的金属和绝缘体特性.零温状态方程计算揭示了在68 GPa时可以发生从单斜结构 关键词： 2')" href="#">VO₂ 相变 第一性原理     

用线性丸盒轨道原子球近似超元胞法计算(Ba_(1-x)K_x)BiO_3立方超导相(x=0.25,0.5,0.75)的电子结构

用线性丸盒轨道原子球近似(LMTO-ASA)超元胞法计算(Ba_(1-x)Kx)BiO_3立方超导相x=0.25与x=0.5的电子结构,作为对照同时计算立方结构x=0.75的电子结构。计算结果表明,用超元胞法可以得到比“刚带近似”较精确的电子结构参数。给出Fermi面上的能带参数随组分的变化趋势。讨论了不等价的氧原子与周围金属原子价轨道的杂化特征。     

用线性丸盒轨道原子球近似超元胞法计算(Ba1-xKx)BiO3立方超导相(x=0.25,0.5,0.75)的电子结构

用线性丸盒轨道原子球近似(LMTO-ASA)超元胞法计算(Ba_1-xKx)BiO₃立方超导相x=0.25与x=0.5的电子结构,作为对照同时计算立方结构x=0.75的电子结构。计算结果表明,用超元胞法可以得到比“刚带近似”较精确的电子结构参数。给出Fermi面上的能带参数随组分的变化趋势。讨论了不等价的氧原子与周围金属原子价轨道的杂化特征。 关键词：     

温稠密氦的状态方程、热输运性质和辐射不透明度的理论研究

温稠密状态下氦元素广泛存在于核聚变内爆过程和宇宙星体中,其热力学性质和辐射输运参数等物质特性在聚变实验设计和星体结构演化研究中起着至关重要的作用.本文采用充分考虑温稠密物质中电子离子碰撞物理效应的量子郎之万分子动力学方法,通过模拟宽广温度密度区域氦离子和电子的响应特性,构建了温度在10-60 kK,密度为1-24 g/cm~3范围内温稠密氦的状态方程数据库和电子热导率数据库,并计算了该温度密度下温稠密氦的辐射不透明度.本文的计算结果可以为聚变物理研究和很多基本天体物理问题建模提供必要的输入参数.     

相结构形成因子统计值对钢中化合物形成的影响

本文根据宏观物理量是微观原子状态统计值的思想,将原子组态最可几值改用统计值代替,利用固体与分子经验电子理论(EET)计算钢中FeS、MnS、TiC(N)、NbC(N)、VC(N)、AlN的相结构形成因子的统计值S^',探讨了各种化合物的S^'对钢中组成原子自发凝聚成各种化合物能力的影响。研究发现S_MnS^'相似文献   

相结构形成因子统计值对钢中化合物形成的影响

本文根据宏观物理量是微观原子状态统计值的思想,将原子组态最可几值改用统计值代替,利用固体与分子经验电子理论(EET)计算钢中FeS、MnS、TiC(N)、NbC(N)、VC(N)、AlN的相结构形成因子的统计值S′,探讨了各种化合物的S′对钢中组成原子自发凝聚成各种化合物能力的影响.研究发现S′McNS′McC,可以从电子层面合理解释钢在平衡状态下由高温向低温转变时,FeS先于MnS析出,合金碳化物先于合金氮化物析出,在非平衡状态下,析出顺序相反的事实.并成功解释了铁碳相图共晶转变和共析转变各个相的形成顺序.从电子层次得出,在平衡条件下,S′较大的相先形成,在非平衡条件下,S′较小的相先形成.在某一适当冷却速度范围内,S′相差较小的相可以共生,这一冷却速度区间将是S′差值的函数.     

三方和四方相PbZr0.5Ti0.5O3 的结构稳定性和电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理超原胞方法和虚晶近似方法, 在局域密度近似和广义梯度近似下系统研究了三方相和四方相 PbZr_0.5Ti_0.5O₃的能量稳定性、原子结构以及电子结构. 计算结果表明三方相的能量比四方相低, 说明三方相结构更加稳定, 并且发现利用广义梯度近似计算的结构参数与实验值符合得更好. 电子结构表明, 两种相的Ti/Zr的3d电子和O的2p电子间存在明显的轨道杂化, 并且Ti-O之间的作用比Zr-O作用更强;Pb的6s和5d电子与O的2s和2p电子也分别存在轨道杂化. 而三方相中Pb的5d电子与O的2s电子杂化比四方相更强, 进一步说明三方相比四方相结构更加稳定.     

钢动静态强度计算的电子理论模型

价电子结构对物性具有本质的影响,以固体与分子经验电子理论为基础,结合材料动态力学过程,构建了计算钢静动态强度的新模型.该模型预测的多种成分钢的静(动)态强度与实验值符合得较好.首次把价电子结构参数引入了材料动态性能的预测模型中.     

AuBe5型新相NdMgNi4-xCox的第一性原理研究

利用密度泛函理论系统研究了AuBe5型新相NdMgNi4-xCox(x=0,1,2,3)的晶体学结构、弹性力学性能、热力学性质和电子结构特性.与试验数据相比,晶格常数的相对误差在0.34％之内,而晶体学参数的相对误差在0.24％之内.通过广义胡可定律、Voigt-Reuss-Hill方法和平均声速计算了弹性常数、弹性模...     

Valence electronic structure of tantalum carbide and nitride

The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent, metallic and ionic characters. For a quantitative analysis of the relative strength of these components, their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN, which coincides to that deduced from the first-principles method.     

Light absorption and excitation energy transfer calculations in primitive photosynthetic bacteria

In photosynthetic organisms, light energy is converted into chemical energy through the light absorption and excitation energy transfer (EET) processes. These processes start in light-harvesting complexes, which contain special photosynthetic pigments. The exploration of unique mechanisms in light-harvesting complexes is directly related to studies, such as artificial photosynthesis or biosignatures in astrobiology. We examined, through ab initio calculations, the light absorption and EET processes using cluster models of light-harvesting complexes in purple bacteria (LH2). We evaluated absorption spectra and energy transfer rates using the LH2 monomer and dimer models to reproduce experimental results. After the calibration tests, a LH2 aggregation model, composed of 7 or 19 LH2s aligned in triangle lattice, was examined. We found that the light absorption is red shifted and the energy transfer becomes faster as the system size increases. We also found that EET is accelerated by exchanging the central pigments to lower energy excited pigments. As an astrobiological application, we calculated light absorptions efficiencies of the LH2 in different photoenvironments.     

Superresolution via enhanced evanescent tunneling

We here propose the concept of enhanced evanescent tunneling (EET). Our analysis indicates that by means of a suitable control field, the transmission of evanescent waves across a forbidden gap can be enhanced by several orders of magnitude-well beyond the ordinary frustrated total internal reflection case. We show how such a phenomenon can be used to probe both the amplitude and phase of the evanescent portion of the angular spectrum, thereby allowing target superresolution. In principle EET can be manifested in other areas of physics where wave tunneling is involved.     

Mössbauer effect of iodine at pressures to 30 GPa

We report the first high pressure¹²⁹I Mössbauer measurements with elemental iodine at pressures to 30 GPa. A 20 mg/cm^{2 129}I₂ absorber was mounted in a diamond anvil cell with an effective diameter of 0.21 mm. The source used was Mg₃ ^129mTeO₆. Experiments were performed mainly at 4 K and the pressure was monitored by the ruby fluorescence method. With increasing pressure we observe a gradual decrease in ¦e²qQ¦ and an increase in IS and values of the low pressure, molecular phase; at 16 GPa a new phase (HP1) is detected characterized by a change in sign of e²qQ and a smaller value of ¦e²qQ¦, and a substantial increase in . At 24 GPa a new phase (HP2) is formed that is characterized by a smaller value of . In general the population of the molecular phase decreases from 1.0 near 15 GPa to a value of 0.4 at 30 GPa. The fraction of the high pressure phase (HP1 + HP2) increases at the expense of the molecular phase and that of the HP2 at the expense of the HP1 phase. These observations are discussed in relation to the onset of a metallic phase near 16 GPa and recent x-ray diffraction studies.Work performed under the auspices of the U.S. Department of Energy.     

Calculation of the surface energy of hcp-metals with the empirical electron theory

A brief introduction of the surface model based on the empirical electron theory (EET) and the dangling bond analysis method (DBAM) is presented in this paper. The anisotropy of spatial distribution of covalent bonds of hexagonal close-packed (hcp) metals such as Be, Mg, Sc, Ti, Co, Zn, Y, Zr, Tc, Cd, Hf, and Re, has been analyzed. And under the first-order approximation, the calculated surface energy values for low index surfaces of these hcp-metals are in agreement with experimental and other theoretical values. Correlated analysis showed that the anisotropy of surface energy of hcp-metals was related with the ratio of lattice constants (c/a). The calculation method for the research of surface energy provides a good basis for models of surface science phenomena, and the model may be extended to the surface energy estimation of more metals, alloys, ceramics, and so on, since abundant information about the valence electronic structure (VES) is generated from EET.     

Calculation of the surface energy of bcc-metals with the empirical electron theory

We have used the dangling bond analysis method (DBAM) based on the empirical electron theory (EET) to establish a database of surface energy for low index surfaces of the bcc-metals such as V, Cr, Fe, Nb, Mo, Ta, and W. And a brief introduction of the new surface energy models will be presented in this paper. Under the first-order approximation the calculated results are in agreement with experimental and other theoretical values. And the calculated surface energy shows a strong anisotropy. As we predicted, the surface energy of the close-packed (1 1 0) is the lowest one of all index surfaces. It is also found that the dangling bond electron density and the spatial distribution of covalent bonds have a great influence on surface energy of various index surfaces. The new calculation method for the research of surface energy provides a good basis for models of surface science phenomena, and the model may be extended to the surface energy estimation of more metals, alloys, ceramics, and so on, since abundant information about the valence electronic structure (VES) can be generated from EET.     

Anomalous energy transfer dynamics due to torsional relaxation in a conjugated polymer

In isolated conjugated polymers two explanations are in discussion for the redshift of the emission on a picosecond time scale-exciton energy transfer (EET) between conjugated segments along the chains and conformational changes of these segments themselves, i.e., torsional relaxation. In order to resolve this question we perform femtosecond time-resolved transient absorption measurements of the energy relaxation of poly[3-(2,5-dioctylphenyl)thiophene] in toluene solution. We show that torsional relaxation can be distinguished from EET by site-selectively exciting low-energy conjugated segments. We present a unified model that integrates EET and torsional dynamics. In particular, comparison to ultrafast depolarization measurements shows that torsional dynamics cannot be neglected when analyzing EET dynamics and furthermore reveals that the exciton extends itself by about 2 monomer units during torsional relaxation.