若干In2Se3 化合物的晶体结构与电子特性

等离激元是金属中自由电子的集体振荡,其在物理,生物、化学、能源、信息等领域具有重要的应用前景。近些年来对等离激元量子效应研究的深入开展使得等离激元研究迈入了新阶段。本文首先简要介绍了等离激元的两个基本特性：光压缩效应和局域电场增强效应;随后回顾了量子等离激元方面的最新的进展,包括量子纠缠效应,量子尺寸效应,量子遂穿效应,等离激元在台阶势垒处的反射与激发,等离激元对电子相干效应的增强;最后对量子等离激元研究进行了总结和展望。     

若干In2Se3化合物的晶体结构与电子特性

In_2Se_3是一种常见的A_2~ⅢB_3~Ⅵ型半导体,在不同温度下可表现出不同的物相,对应的晶格参数与物理性质也会有所不同.在过去几十年间,In_2Se_3的多相性引起了人们的关注,各物相的晶体结构被广泛地研究.近年来,研究发现α-In_2Se_3具有优异的光电、压电性能以及独特的铁电性能,可以预见它将在未来的半导体电子器件中发挥出重要的作用.本文综述了一系列In_2Se_3化合物的晶体结构与电子特性,我们首先简要介绍了这些In_2Se_3化合物的基本知识,接着详细讨论了它们的晶体结构与电子特性,最后对In_2Se_3化合物的研究前景进行了展望.     

一维金属/介质光子晶体用于BaF2晶体闪烁光谱修饰

利用一维金属/介质光子晶体对BaF2晶体闪烁光谱进行修饰. 以Al2O3/MgF2/Al/ MgF2为周期构成光子晶体，讨论了周期数、金属层的厚度以及在低折射率层中的相对位置、入射角度等与光子晶体能带特性的关系及其对BaF2晶体闪烁光谱进行修饰的效果. 结果表明，在所考虑的发射角范围，光子晶体对快成分的衰减小于5倍，对慢成分的相对抑制比超过20倍，采用合适的探测角度，可使对慢成分的相对抑制比提高到100以上.     

Impurity induced interactions in diluted La2CuO4

A non-magnetic impurity, such as Zn, doped into a non-frustrated antiferromagnet can induce substantial frustrating interactions among the spins surrounding it and result in an enhanced suppression of the antiferromagnetic order. In addition, the strength of the intra-plane exchange couplings surrounding impurities is reduced by the lattice distortions. Using quantum Monte Carlo, we calculate the initial suppression rate of the staggered magnetization in a two-dimensional diluted Heisenberg antiferromagnet with both frustrating interaction and lattice distortion induced by the impurity. We find that the lattice distortion alone cannot explain the experimental results, while the dominant effect of enhanced order suppression is due to the frustrating interaction.     

低对称层状ReS2的电子结构和各向异性光学性质研究

采用第一性原理赝势平面波方法计算了三斜晶系低对称层状半导体二硫化铼（ReS2）的晶体结构、电子结构及光学性质。结果表明：扭曲的1T结构为ReS2的稳定结构, Re原子与其周围的S原子形成六配位的近似八面体结构,Re-S键长最大偏差为8.3%,Re-S键布局数最大偏差为40.5%,表明ReS2结构的低对称性;ReS2为直接带隙半导体,费米面附近的价带和导带主要由Re的5d及S的3p轨道电子构成,其中Re的5d轨道电子的贡献最大;当入射偏振光沿着[100]和[010]方向时,介电函数的实部（或虚部）非常接近,而当入射偏振光沿[001]方向时,介电函数的实部（及虚部）表现出明显的各向异性,主要是由于ReS2的结构低对称性和弱层间耦合造成的。     

S-酮洛芬电子结构及手性光谱性质的理论研究

采用DFT及TD-DFT方法在B3LYP/6-311++G**水平对S-酮洛芬电子结构及手性光学性质进行了理论研究. 研究发现,羰基与两个苯环发生共轭;由于C(20)与C(11)上H原子之间存在空间位阻,羰基与环A及环B之间均存在一定的二面角. VCD谱中,标题化合物在1216和1712 cm-1处存在负性康登效应;在733、1803、1465和3751 cm-1处存在正性康登效应. C(14)=O(21)和C(4)=O(5)伸缩振动的空间方向相反,在VCD谱上的康登效应符号也刚好相反. 甲醇溶液中,S-酮洛芬在214、334 nm处存在负性康登效应,在226、274 nm处存在正性康登效应. 214和226 nm、274和334 nm处的电子转移方向分别相反,在ECD谱上呈现出符号相反的康登效应.     

Electronic States and Spatial Charge Distribution of Single Mn Impurity in Diluted Magnetic Semiconductors

The electronic and magnetic properties as well as the spatial charge distribution of single Mn impurity in III--V diluted magnetic semiconductors are obtained when the degeneracy of the p orbits contributed from the four nearest-neighbouring As(N) atoms is taken into account. We show that in the ground state, the Mn spin is strongly antiferromagnetically coupled to the surrounding As(N) atoms when the p-d hybridization V_pd is large and both the hole level E_v and the impurity level E_d are close to the Fermi energy. The spatial charge distribution of the Mn acceptor in the (110) plane is non-spherically symmetric, in good agreement with the recent STM images.     

La2与LanF（n＝1,2）分子的结构与势能函数

采用密度泛函理论确定La₂与La_n F（n=1,2）分子的电子与结构特性.应用最小二乘法拟合出La₂和LaF分子的Murrell-Sorbie势能函数,在此基础上推导出光谱数据和力常数.基态La₂F分子具有C_2v对称性的弯曲结构,电子态⁴A₂,结合能为7.89 eV.用多体项展式理论得出La₂ F的解析势能函数,其等值势能图准确再现了La₂ F分子的平衡结构.     

CuI晶体及其缺陷态电子结构的模拟

利用相对论密度泛函理论和嵌入分子团簇方法,模拟计算了具有闪锌矿结构的γ态CuI晶体及其缺陷态的电子结构。结果显示晶体的本征能级结构:价带顶主要由I5p和Cu3d轨道杂化组成,导带底由Cu4s轨道组成,禁带宽度为3.1eV,该结果与实验相符。在不同缺陷态的计算中,四面体间隙铜缺陷相对其他间隙缺陷更易于在晶体中形成,其中Cu3d→4s跃迁能量为3.2eV,推测与CuI晶体发光密切相关。     

钼酸铅晶体中F型色心电子结构的理论计算

运用相对论性的密度泛函离散变分(DV-Xα)方法模拟计算PbMoO₄晶体中可能存在的F型色心的电子结构.结果表明,F,F⁺心在PbMoO₄晶体的禁带中引入了施主能级,其光学跃迁能分别是2.141,2.186 eV,即F,F⁺心能分别引起PMO晶体中581,567 nm的吸收,该吸收与PbMoO₄晶体中580 nm的吸收峰对应.因此,可推断F型色心能引起PMO晶体中由光色效应引起的580 nm吸收.     

含色心BaMgF4晶体电子结构的研究

运用相对论性的密度泛函离散变分法(DV-X)研究BaMgF4晶体中F型色心的电子结构.计算中采用冻结原子核的H原子模拟F心,在DV-Xα源程序增加H原子2p态,使F心激发态的计算结果在物理上更加合理.计算结果表明,F心的基态和激发态均出现在禁带中;并用过渡态的方法计算得到F心的电子从基态到激发态的光学跃迁能量为5.12eV,对应242nm处的吸收带,计算结果与实验结果吻合得很好,因此,推测F心在BaMgF4晶体中引起236～274 nm的吸收.     

Theoretical Studies on Electronic Structures and Spectroscopy of Fluorescent Arylamino Fumaronitrile

设计了一系列发荧光的芳胺氰化物, 并用密度泛函方法在B3LYP/6-31G*水平上进行几何构型优化．在优化构型基础上,分别用INDO/CIS、AM1、CIS-ZINDO TD和B3LYP/6-31G*方法计算了芳胺氰化物的电子光谱、红外光谱、荧光光谱及核磁共振碳谱．结果表明,与母体相比,由于萘环较大的立体效应使氰化物的能隙变宽,荧光光谱及电子光谱的主要吸收峰发生蓝移．而由于电子被分散到萘环上,氰化物的主要红外频率发生红移．相反,羟基的存在改善了分子的对称性,扩展了共轭体系,使能隙变窄,荧光光谱及电子光谱的主要吸收峰发生红移．同时由于羟基的供电效应,C-H伸缩振动发生蓝移．     

Investigation of the Scintillation Properties of Domestic BaF2(La) Crystal

BaF₂(La) crystal has been grown with 1% mole of BaF₃ doped in BaF₂ and the scintillation properties of the new crystal have been investigated before and after a γ irradiation of ⁶⁰Co source.The radiation resistance of the domestic crystal can be up to a dose of 10⁶ rad.Comparing with a pure BaF₂ scintillator,it was found that the fast component of the BaF₂(La) scintillator was almost no change but its slow component was suppressed to a factor of 4.     

掺铜PTO晶体顺磁共振谱及局域结构的理论研究

基于晶体场理论,本文采用重叠模型和3d⁹电子组态在畸变四角晶场中的g因子和超精细结构常数A的三阶微扰计算公式以及钛酸铅PbTiO₃ (PTO): Cu²⁺晶体的局域结构与EPR谱之间的定量关系,合理解释了PTO: Cu²⁺晶体的EPR谱及局域晶体结构,所得结果与实验观测相符合.      

Experimental Investigation of Electronic Structure of La(O,F)BiSe_2

La(O,F)BiSe2 is a layered superconductor and has the same crystal structure with La(O,F)BiS_2.We investigate the electronic structure of La(O,F)BiSe2 using the angle-resolved photoemission spectroscopy.Two electron-like Fermi surfaces around X(π,0) are observed,corresponding to the electron doping of 0.23 per Bi site.We clearly resolve anisotropic band splitting along both Γ~X and M-X due to the cooperative effects of large spin-orbit coupling and interlayer coupling.Moreover,we observe an almost non-dispersive electronic state around-0.2eV between the electron-like bands.This state vanishes after in-situ K evaporation,indicating that it could be the localized surface state caused by defects on the cleaved surface.     

镧掺杂对锐钛矿TiO2电子结构与光催化活性影响的第一性原理研究

基于DFT+U方法,对镧掺杂锐钛矿TiO₂及其氧空缺的稳定性以及对电子结构、光催化性质的性质进行了第一性原理研究．计算结果表明掺杂浓度和位置对结构稳定性的影响机制符合鲍林规则;结合晶体场理论和结构形变以及态密度的分析发现镧掺杂对带隙的调制不是通过掺杂带的引入,而是由结构形变决定．吸收光谱的模拟结果显示通过镧掺杂会提高可见光的吸收效率,和实验结果吻合．对氧空缺的后续研究表明氧空缺的存在会增强镧掺杂锐钛矿TiO₂的稳定性,提高其光催化活性．     

Electronic structure of La2CuO4

The electronic band structure of La₂CuO₄ is performed using self-consistent linear muffin-tin orbital method. The 17 band complex is found to arise mainly from the overlap between Cu-3d and O-2p wavefunctions. The calculated density of states at the Fermi energy (N E _F), the conduction band-width and the electronic specific heat coefficient are given.     

Theoretical and Experimental Investigation of the Formation of High Spatial Frequency Periodic Structures on Metal Surfaces Irradiated by Ultrashort Laser Pulses

Experimental results on the formation of small-scale periodic nanostructures during ablation of solids by pico- and femtosecond laser pulses are presented. The period of these nanostructures is in the range of 50 to 100 nm, and they may coexist with known periodic nanostructures, whose period and orientation is determined by the laser wavelength and amounts to several hundreds of nanometers. The formation of high-frequency periodic structures with a period of about 100nm is theoretically analyzed by joint numerical solution of the heat conduction problem and Navier?Stokes equation. It is shown that their orientation is determined by the melt bath geometry.     

Effect of hydrostatic and chemical pressure on BaF2 and BaF2: Eu2+ crystals

The effect of hydrostatic pressure on a BaF₂ crystal was studied within the shell model in the pair-wise potential approximation. The structural phase transition from the cubic to orthorhombic phase was simulated. The behavior of the unit-cell parameters of the α-and β-BaF₂ phases under hydrostatic pressure (from 0 to 12 GPa) was investigated. The fundamental vibration frequencies of BaF₂ under hydrostatic pressure (0–3.5 GPa) were calculated for both phases. The effect of chemical pressure on the BaF₂ crystal was studied by simulating Ba_1?x Me_xF₂ mixed crystals (Me=Ca, Sr). It was shown that at impurity concentrations up to 15–20 at. % the lattice constant varies in the same way as it does when hydrostatic pressure increases to P _c , which corresponds to a phase transition to the orthorhombic phase. The effect of chemical and hydrostatic pressure on BaF₂: Eu²⁺ doped crystals was also studied. The dependence of the absorption and luminescence zero-phonon line shift on the Eu²⁺-ligand distance was calculated.