立方钙钛矿RbZnF3电子、弹性和光学性质的第一性原理研究

基于密度泛函理论和赝势平面波方法研究了立方钙钛矿RbZnF3的电子结构和光学性质;利用静水有限应变技术计算研究了RbZnF3弹性常数Cij、体积弹性模量B和剪切模量G随压力的变化关系。基态下,RbZnF3晶格常数a和体积弹性模量B0计算值与实验值以及其他理论值一致。根据能带结构、总态密度以及分波态密度分析可知：基态下立方钙钛矿结构RbZnF3为间接带隙半导体材料,带隙为3.57eV,与其他计算结果比较,本文计算结果偏低,这是由于局域密度近似(LAD)或广义梯度近似(GGA)交换关联函数的局限性所致。基态下RbZnF3的Mulliken电荷分布和集居数说明：RbZnF3属于共价键和离子键所形成的混合键化合物;RbZnF3的电荷总数主要来源于Rb 4s和4p轨道,Zn 3d轨道,以及F 2s和2p轨道。电荷主要从Rb, Zn原子向F原子转移。同时,本文还计算研究了RbZnF3的光学介电函数、吸收系数、复折射率、能量损失谱和反射系数等光学性质。     

立方钙钛矿RbZnF_3电子、弹性和光学性质的第一性原理研究

基于密度泛函理论和赝势平面波方法研究了立方钙钛矿RbZnF_3的电子结构和光学性质;利用静水有限应变技术计算研究了RbZnF_3弹性常数Cij、体积弹性模量B和剪切模量G随压力的变化关系.基态下,RbZnF_3晶格常数a和体积弹性模量B0计算值与实验值以及其他理论值一致.根据能带结构、总态密度以及分波态密度分析可知:基态下立方钙钛矿结构RbZnF_3为间接带隙半导体材料,带隙为3.57eV,与其他计算结果比较,本文计算结果偏低,这是由于局域密度近似(LAD)或广义梯度近似(GGA)交换关联函数的局限性所致.基态下RbZnF_3的Mulliken电荷分布和集居数说明:RbZnF_3属于共价键和离子键所形成的混合键化合物;RbZnF_3的电荷总数主要来源于Rb 4s和4p轨道,Zn 3d轨道,以及F 2s和2p轨道.电荷主要从Rb,Zn原子向F原子转移.同时,本文还计算研究了RbZnF_3的光学介电函数、吸收系数、复折射率、能量损失谱和反射系数等光学性质.     

YFe2B2电子结构的第一性原理计算

基于密度泛函理论,从头计算了具有ThCr₂Si₂型四方晶系的稀土金属化合物Yfe₂B₂体相的物理特性.能量计算结果表明Yfe₂B₂体相处于顺磁金属态;而能带结构、态密度、布居数以及差分电荷　分布的计算结果表明Y原子的5s,5p电子具有很强的局域性;Fe原子的3d电子和B的1s,2s和2p电子强烈耦合,使得最近邻Fe原子与B原子形成了Fe—B共价键;最近邻的两个Fe原子之间由于 关键词： 稀土金属化合物 第一性原理计算 能带结构 态密度     

原子的价壳层激发态波函数和跃迁特性

本文探讨了快电子碰撞下判别原子跃迁多极性的方法,指出了从实验上由广义振子强度比和光学振子强度比及中间耦合系数的归一化特性来确定中间耦合系数的方法.然后以氩原子为例,计算了其价壳层激发的中间耦合系数,并在2500 eV入射能量下实验测量了氩原子跃迁到3p54s[3/2]1和3p54s′[1/2]1的广义振子强度比,在此基础上阐明了氩原子价壳层激发的多极性,从实验上获得了氩原子3p54s[3/2]1和3p54s′[1/2]1的中间耦合系数.本文得出了LS耦合的波函数足以描述氩原子的光子或快带电粒子碰撞激发过程的结论,这是由于氩原子基态的LS耦合特性在快电子激发过程中选择了激发态波函数中的单态成份决定的.并指明该结论可以推广到描述其它原子的光子或快带电粒子的碰撞激发过程.     

Rb(7D)+Na(3S)碰撞激发转移过程

研究了Rb Na异核系统的能量碰撞合并逆过程 (REP)。两步激发Rb原子到 7D3 / 2 态。应用双调制技术探测Na(3Pj)原子发射的荧光 ,基态Na原子密度用光学吸收方法测量。得到了REP率系数 ,讨论了其他过程对率系数的影响。     

激光激发Cs+H_2系统形成CsH分子机理的实验研究

在Cs-H2混合系统中用激光将Cs原子激发到6P3/2能级,研究了CsH分子的形成机制.利用光学吸收法得到6P3/2态的密度及其空间分布,能量合并过程6P3/2+6P3/2→6D+6S1/2产生6D态原子;猝灭过程Cs(6P3/2)+H2(v=0)→Cs(6S1/2)+H2(v=2)产生H2(v=2)态.由6P3/2态原子密度及6D→6P3/2与6P3/2→6S1/2的荧光比得到碰撞能量合并速率系数,在不同的H2密度下,测量了转移荧光强度I895,得到了H2(2,J)态的产生速率系数kH2(2,J)=1.     

A-La2O3电子结构和光学性质的第一性原理计算

采用基于密度泛函理论(DFT)框架下广义梯度近似平面波超软赝势法,计算A-La2O3的电子结构和光学性质.结果表明,A-La2O3,属于间接带隙氧化物,禁带宽度为3.72 eV;其价带主要由La的5s,5p和6s态电子以及O的2s和2p态电子构成,导带主要由La的5d态电子构成.经带隙校正后,计算得到A-La2O3在(100)和(001)方向上的光学线性响应函数随光子能量的变化关系,包括复介电函数、复折射率、吸收光谱、反射光谱、损失函数和光电导谱.结果表明,A-La2O3,在(100)和(001)方向上具有光学各向异性,并且具有从近紫外到红外的透明区域,为A-La2O3,的应用提供了理论依据.     

Nd(Fe,Si)11Cx化合物的全电子计算(x=0,2)

采用基于第一原理的全势能线性缀加平面波加局域轨道((L)APW lo)方法对Nd(Fe,Si)11Cx化合物(x=0,2)的电子结构进行了计算,得到了化合物态密度和磁矩等信息.计算结果表明NdFe9Si2化合物中Si原子主要与4b和32i位Fe原子产生杂化,导致Fe原子磁矩减小.NdFe9Si2C2化合物C原子使32i位Fe原子磁矩进一步降低,同时减弱了Si原子的影响,使得4b位Fe原子磁矩增大.     

原子光学讲座第二讲量子原子光学

近年来,有关玻色一爱因斯坦凝聚（BEC）及其量子光学性质的理论与实验研究得到了飞速发展,并取得了一系列重大进展,从而形成了一门原子光学的新分支学科——“量子原子光学”．文章重点介绍了量子原子光学的研究内容、实验结果及其最新进展,主要包括BEC实验研究的重大进展、原子量子态的实验制备、原子激光的产生及其最新进展、BEC凝聚体或原子激光的相干性和费米原子气体的量子简并等．     

Cs(8D,9D)+Na(3S)碰撞激发转移过程

此文报道异核Cs(8D,9D)+Na(3S)→Cs(6P)+Na(3P)的碰撞能量转移过程.两步激发Cs原子到9D3/2(8D3/2)态.应用双调制技术探测Na(3PJ)原子发射的荧光,基态Na原子密度用光学吸收方法测量.得到了REP率系数,讨论了其它过程对率系数的影响.     

第一性原理研究H_2O分子在CaCO_3(104)表面吸附

基于密度泛函理论的第一性原理方法模拟研究H_2O在CaCO_3(104)表面的吸附特征.首先,研究H_2O分子在CaCO_3(104)表面的顶位、桥位(短桥位、长桥位)和穴位上垂直和平行表面两种类型下的8种高对称吸附结构模型,结合吸附能和稳定吸附构象确定最优吸附位.而后,基于H_2O/CaCO_3(104)最优吸附结构模型,研究吸附前后H_2O和CaCO_3(104)表面的物理结构、电子结构(Mulliken电荷布居数、态密度、电子局域函数)的特征,分析H_2O/CaCO_3(104)表面之间的相互作用以及成键机理.研究结果:吸附能和体系稳定构象显示H_2O分子/CaCO_3(104)表面的最稳定吸附结构为穴位-平行.在穴位-平行位吸附后,H_2O分子的O-H键长和H-O-H键角均发生改变; CaCO_3晶体平行和垂直(104)表面方向上原子位置均发生改变,表面层变化最大;即吸附作用对H_2O分子和CaCO_3晶体的物理结构均产生较大影响; H_2O/CaCO3(104)最优吸附体系的Mulliken电荷布居数、电子态密度、电子局域函数的研究均说明H_2O分子与CaCO3(104)之间存在电子的转移形成化学键.其中,Ca-O(H_2O)形成离子键,H(H_2O)-O(CaCO_3)之间存在氢键作用.本文研究揭示了方解石表面水湿性的原因,同时为方解石润湿性的深入研究奠定基础.     

武定恐龙化石的显微拉曼光谱研究

本文首次利用激光显微拉曼光谱、原子光谱和偏光显微镜等方法 ,对云南武定的恐龙化石进行了分析研究。实验发现 ,恐龙化石表面和截面的拉曼光谱 ,均为典型的方解石 (CaCO3 )晶体的拉曼谱 ,并未发现有其他成分的拉曼谱。原子发射光谱的分析结果表明 ,恐龙化石中的主要元素有Ca(>10 % ) ,其次是Si(5 0 % )和P(4 0 % ) ,还有Fe(1 0 % )等 ,但未发现铱、钍等稀有元素。由恐龙化石截面在偏光显微镜下的图像可以知道 ,恐龙化石表面层的成分主要是方解石晶体 ;内部的主要成分为方解石 (CaCO3 )晶体 ,此外还有纤维状一水二氧化硅 (分子式SiO2 ·nH2 O ,属非晶态 )等成分。激光拉曼光谱能快速无损地准确检测出恐龙化石的主要成分是方解石 (CaCO3 ) ,拉曼光谱对恐龙化石的分析结果与原子光谱、偏光显微镜的分析结果是一致的     

SO2在CaCO3颗粒表面转化的DRIFTS研究

碳酸钙 (CaCO3 )是大气中矿物颗粒物的重要组分 ,其非均相大气化学行为很不清楚。利用原位漫反射红外傅里叶变换光谱 (DiffuseReflectanceInfraredFourierTransformSpectroscopy ,DRIFTS)研究了二氧化硫(SO2 )在CaCO3 颗粒物表面的转化情况。通过比较不同条件下 ,亚硫酸盐和硫酸盐的原位光谱 ,探讨了SO2在CaCO3 表面氧化中臭氧 (O3 )所起的作用。结果表明 ,利用DRIFTS原位分析反应器研究CaCO3 表面硫酸盐的生成是可行的。在存在O3 条件下 ,SO2 在CaCO3 表面能够被氧化成硫酸盐 ,反应分为吸附和氧化两个步骤进行。     

New ways of probing surface nuclear relaxation and microdynamics of water and oil in porous media.

The microdynamics of water and oil in macroporous media with SiO2 or CaCO3 surfaces has been probed at various temperatures by magnetic field-cycling measurements of spin-lattice relaxation rates. These measurements and an original theory of surface diffusion allow us to obtain surface dynamical parameters such as surface correlation times, residence times and diffusion coefficients. A coefficient of affinity of the liquids for the pore surface is deduced.     

NH_3多相氧化的实验研究

1引言煤燃烧过程中特别是流化床中为了减少SOZ的排放，一般采用向炉内加入石灰石等添加物的方法。这些添加物质的存在，使挥发分含氮物质的氧化机理异于纯单相氧化。因此研究钙基脱硫剂（CaCO。）及其生成物（CaSO。、煤灰）对NH。和HCN的多相氧化有助于了解实际锅炉煤燃烧过程中脱硫对氮氧化物生成的影响。Lin［‘］研究了石灰石和CaSO。对NH。氧化的影响。发现石灰石对NH。氧化生成NO具有相当大的催化作用，可使NH3MNO的转化率达65％，而C3SO4存在和空管时NH3氧化结果一致，表明CaSO。对NHa无氧化作用。IisJ‘」在研究Ca…     

Atom-molecule collisions in an optically trapped gas

Cold inelastic collisions between confined cesium (Cs) atoms and Cs2 molecules are investigated inside a CO2 laser dipole trap. Inelastic atom-molecule collisions can be observed and measured with a rate coefficient of approximately 2.6 x 10(-11) cm3 s(-1), mainly independent of the molecular rovibrational state populated. Lifetimes of purely atomic and molecular samples are essentially limited by rest gas collisions. The pure molecular trap lifetime ranges 0.3-1 s, 4 times smaller than the atomic one, as is also observed in a pure magnetic trap. We give an estimation of the inelastic molecule-molecule collision rate to be approximately 10(-11) cm3 s(-1).     

Microscopical and functional aspects of calcium-transport and deposition in terrestrial isopods

Terrestrial isopods (Crustacea) are excellent model organisms to study epithelial calcium-transport and the regulation of biomineralization processes. They molt frequently and resorb cuticular CaCO(3) before the molt to prevent excessive loss of Ca(2+) ions when the old cuticle is shed. The resorbed mineral is stored in CaCO(3) deposits within the ecdysial gap of the first four anterior sternites. After the molt, the deposits are quickly resorbed to mineralise the posterior part of the new cuticle. The deposits contain numerous small spherules composed of an organic matrix and amorphous CaCO(3), which has a high solubility and, therefore, facilitates quick mobilization of Ca(2+) and HCO(3)(-) ions. During the formation and resorption of the deposits large amounts of Ca(2+), HCO(3)(-) and H(+) are transported across the anterior sternal epithelial cells. Within the last years, various light and electron microscopical techniques have been used to characterize the CaCO(3) deposits and the cellular mechanisms involved in biomineralization. The work on the CaCO(3) deposits includes studies on the ultrastructure of the deposits, the sequence of events during deposit formation and dissolution, and the mineral composition of the sternal deposits. The differentiation of the anterior sternal epithelial cells and the mechanisms of epithelial ion transport required for the mineralization and demineralisation of the deposits was studied using various analytical light and electron microscopical techniques including polarized light microscopy, immunocytochemistry, electron microprobe analysis, electron energy loss spectroscopy and electron spectroscopic imaging. Comparative analysis of deposit morphology and the differentiation of the sternal epithelia provide information on the evolution of CaCO(3) deposit formation in relation to the degree of adaptation to terrestrial environments.     

钠分子B^1∏u与2^1∑g^＋间的碰撞激发转移

The B 1pi(u) electronic state of Na2 was excited by the 441.6 nm He-Cd laser line. The Na atomic transitions and the A 1sigma(u)+ --> X 1sigma(g)+ band of Na2 were recorded. From the intensities and spectra of the Na and Na2 fluorescence several collisional processes in the excited sodium atom-dimer system were identified. The Na atomic lines are the result of collisional energy transfer from Na2 (B 1pi(u)) to Na(3P). Predissociation process may also contribute to atomic fluorescence. The A 1sigma(u)+ --> X 1sigma(g)+ band is interpreted through a populating mechanism involving collisional transfer from B 1pi(u) to 2 1sigma(g)+ followed by a radiative transfer to the A 1sigma(u)+ state. From the decay constants and fluorescence intensities, the rate coefficient at 360 degrees C for collisional energy transfer from Na2 (B 1pi(u)) to Na2 (2 1sigma(g)+) was found to be 5.7 x 10(-10) cm3 x s(-1). The predissociation rate of the B 1pi(u) is 2.7 x 10(6) s(-1).     

Thermal and chemical approaches for oxygen catalytic recombination evaluation on ceramic materials at high temperature

During the atmospheric entry phase, the physico-chemical phenomena taking place on space shuttle walls can lead to an important excess of heating and damage of the protective materials. The aim of this work is the study of the catalytic recombination of atomic oxygen under plasma conditions chosen to simulate the atmospheric reentry. To do that, we have developed an experimental set-up MESOX (Moyen d'Essai Solaire d'OXydation), which associates a solar radiation concentrator and a microwave generator to reach high temperature, low enthalpy flow and low pressure plasma with an air gas flow. The study of atomic oxygen recombination on silicon- or aluminum-based ceramic materials, at high temperature (1000–1800 K) has been done for different pressures (200–2000 Pa) by a thermal and a chemical understanding. The results give a catalycity scale of materials (thermal recombination flux, q_rec, and coefficient of atomic oxygen recombination, γ). The catalycity activity is weak for the sintered SiC target with atomic oxygen recombination flux reaching 35 kW/m², however, for a target of sintered Al₂O₃, catalytic effect is obtained with energy fluxes between 90 to 180 kW/m². The recombination coefficient γ confirms the catalycity scale of these ceramic materials.     

Observation of pair absorption in calcium

Pair absorption has been observed in calcium using broad band absorption. The absorption peaks at the sum energy of the (4s4p) ¹P° and (4s3d) ¹D atomic states. A cross section of 1.3 × 10^-22 (P/A) cm² is measured corresponding to a reduced absorption coefficient of 1.3 × 10^-35 cm⁵. An error in earlier calculations predicting the reduced absorption coefficient for pair absorption in barium is noted. Simple scaling laws, our experimental results, and the assumption that the barium process is dominated by the resonant dipole-dipole interaction are used to deduce an upper limit for the calcium (4s3d) ¹D→(4s4p) ¹P° oscillator strength of 6.5 × 10^-4.