O3+与H2碰撞中非解离电荷转移过程的全量子计算

应用全量子的分子轨道强耦合方法，研究了基态的O³⁺(2s²2p ²P)与氢分子碰撞的非解离电荷转移过程，计算了不同方位角(25°，45°，89°)，能量分别为100，500，1000和5000eV/u时的单电子俘获的振动分辨的态选择截面及相应的微分截面.分子轨道强耦合计算中采用了自旋耦合价带理论计算的三原子分子势能面和径向耦合矩阵元.对氢分子的自身转动，采用无限阶的冲量近似方法；对体系的电子运动同H₂或H^+<     

双层反铁磁体K3Cu2F7 中轨道序驱动的自旋二聚化

基于自旋-轨道-晶格Hamilton量,应用团簇自洽场方法,研究了双层钙钛矿结构材料K₃Cu₂F₇基态的晶格、磁及轨道结构,发现近孤立的双层的对称破缺和Jahn-Teller晶格畸变使得Cu²⁺离子在每层内交替占据 z²-x²〉/ z²-y²〉轨道,进而导致双层的层间表现为强的反铁磁耦合,层内为弱的铁磁耦合.强反铁磁耦合导致层间     

基于同轴TM812模谐振腔的毫米波多注速调管

 研究了群聚电子注穿越同轴TM₈₁₂模谐振腔的换能效率和同轴TM₈₁₂模谐振腔中微波能量的提取方法,论证了其作为毫米波多注速调管的输出腔的可行性。研究结果表明:理想群聚电子注穿越同轴TM₈₁₂模谐振腔的换能效率可达3.29%,一般群聚电子注穿越同轴TM₈₁₂模谐振腔的换能效率可达1.86%;采用同轴TM₈₁₂模谐振腔与沿轴向的同轴线耦合可以实现微波能量的提取;在输出腔工作频率为100.945 GHz,外观品质因数为2 243情形下,根据估算,最大输出功率可达15 kW。     

应变作用下量子顺电材料EuTiO3的磁电性质

由于磁性和介电性质的强烈耦合, 量子顺电材料EuTiO₃材料的研究近来倍受人们的关注. 本文通过运用基于密度泛函理论的第一性原理计算研究了量子顺电(PE) 材料EuTiO₃的磁性和电子结构, 分析了应变对磁性和结构相变的作用, 从而探讨了该材料中可能的磁电耦合机理. 结果发现, 在无应变状态下, EuTiO₃处于顺电立方-G型反铁磁性态, 而对于c轴方向的无论张应变还是压应变, 当应变增加到一定程度时, 由于Ti 3d空轨道与周围O 2p 电子的杂化平衡被打破, EuTiO₃将相变到铁电( FE) 四方-铁磁结构, 显示了强烈的自旋-晶格耦合效应.     

长周期光纤光栅中的包层模谐振

本文给出了光纤中包层模的电场形式,指出包层膜的电场形式与弱导光纤中导模的电场形式不同,对光纤中基模与包层模电场沿光纤横截面分布的重叠情况的分析表明,长周期光纤光栅除了能将HE₁₁导模耦合到HE_1p包层模外,也可以将其耦合到EH_1p包层模。基于耦合模理论的计算表明,耦合到EH_1p和EH_1,p-1包层模的耦合波长相近,对于典型的单模光纤,当p>4时耦合到这两个模式的耦合系数是可比的。     

两耦合半无限超晶格中的局域界面声子-极化激元

采用转移矩阵方法，研究了含结构缺陷层的两耦合半无限超晶格(GaAs/AlAs)中的局域界面声子-极化激元模性质. 研究发现，含不同介电特性的缺陷超晶格结构中的局域界面声子-极化激元模在剩余射线区［ω_TO, ω_LO］的分布情况与数量存在不同，而且反对称模表现出不同的特征. 文中着重研究了缺陷层介电常数与角频率无关的缺陷超晶格，发现该结构中的局域界面声子-极化激元模对组分层的排列顺序与厚度、缺陷层的厚度以及横向波数有着不同程度的依赖.     

(InAs)1/(GaSb)1超晶格原子链的第一原理研究

利用第一原理平面波赝势法, 对(InAs)₁/(GaSb)₁超晶格原子链的原子结构、力学特性、电子能带结构、 声子结构和光学特性进行研究, 并结合密度泛函理论数值原子轨道赝势法和非平衡格林函数法计算量子输运特性. 与二维层结构的(InAs)₁/(GaSb)₁超晶格相比, (InAs)₁/(GaSb)₁超晶格原子链的能带结构有明显不同, 在某些情况下表现为金属能带特性. 对理想条件下(InAs)₁/(GaSb)₁ 超晶格原子链的力学强度计算表明, 该结构可承受的应变高达 ε=0.19. 通过对声子结构的完整布里渊区分析, 研究了(InAs)₁/(GaSb)₁超晶格原子链的结构稳定性. 对两端接触电极为Al纳米线的InAs/GaSb超晶格原子链的电子输运特性计算表明, 电导随链长和应变的改变而发生非单调变化.光吸收谱的计算结果表现出在红外波段具有陡峭吸收边, 截止波长随超晶格原子链的结构而变化.预计InAs/GaSb超晶格原子链可应用于红外光电子纳米器件, 通过改变超晶格原子链的结构来调节光电响应波段.     

Ni2+掺杂到氟化物钙钛矿中的局域结构畸变和基态分裂的理论研究

基于双自旋轨道耦合系数模型并结合完全能量矩阵的方法,研究了AMF₃(A=K, Rb; M=Zn, Cd, Ca):Ni²⁺和K₂ZnF₄:Ni²⁺体系中Ni²⁺的基态分裂和局域结构． 通过模拟光谱和电子顺磁共振(EPR)谱,结果显示在研究氟化物络合分子的能级精细结构和局域结构畸变时,配体F^-对体系的自旋轨道耦合机理的影响不可忽略,同时讨论了EPR参量随夹角、自选轨道耦合、平均参量以及偏离参量的变化规律.     

回旋速调管输入耦合器分析与设计

 对Ka波段工作模式为TE₀₁模和TE₀₂模的两种回旋速调管的输入耦合器进行了详细研究，利用模式匹配理论和HFSS建模仿真计算了内圆柱腔和外同轴腔的尺寸；提出了一种与软件计算相结合的模式纯度计算方法，对内腔工作模式纯度、内外腔能量分数进行了计算。内腔侧面上的耦合缝的大小、角向位置都直接决定外同轴腔内的TE_m11模向内圆柱腔的TE_0n1模的耦合情况。针对耦合缝与输入波导成45°和0°分布两种情况，研究了耦合缝长、宽和角向偏移，以及内外腔频差对频率、Q值及内腔能量分数的影响。分别设计了Ka波段内腔工作模式为TE₀₁₁、外腔为TE₄₁₁和内腔TE₀₂₁、外腔TE₈₁₁的两种输入耦合器，并利用矢量网络分析仪对内腔工作模式为TE₀₁₁的耦合器进行了冷高频测量，测得频率为34.257 GHz，与计算结果34.300 GHz仅相差43 MHz。     

Ⅰ类和Ⅱ类准周期半导体超晶格的电子子带和波函数

本文将包迹函数近似推广用于计算有理数近似下,垂直于超晶格轴的波矢K_⊥不等于零时,准周期半导体超晶格(QSS)的电子子带和波函数,对K_⊥=0的情形,分别计算了Ⅰ类的GaAs/Al_xGa_1-xAs和Ⅱ类的InAs/GaSb QSS的电子子带和波函数,直至代序数m=9和6。对于价带对导带影响强的InAs/GaSb QSS,分别计算了m=5和6时电子子带随K_⊥的变化关系。并提出了利用本文结果计算Ⅰ类的GaAs/Al_xGa_1-xAs QSS带间集体激发的具体方法。     

A new approach to analyse H⊗(2h⊕g) Jahn-Teller system for C60

It is now well-known that electron (hole)-vibron coupling and hence Jahn-Teller (JT) effect is important understanding the properties of C₆₀ and related molecules. In this paper, we study H(2) coupling case to find the potential energy surfaces for the positively charged C₆₀ molecule due to distortion. The H(2) Jahn-Teller system is of particular importance as this will be the JT effect displayed by C₆₀ molecules removed with an electron. C₆₀ ⁺ is obtained by removing one electron from fivefold degenerate H_u highest occupied molecular orbital (HOMO) and a hole in HOMO interacts with the vibrational modes of C₆₀ and symmetry is broken. We apply the method of symmetry breaking mechanism to obtain expressions for the potential energy surface. Received 27 December 1999 and Received in final form 15 May 2000     

Manifestation of the Jahn-Teller effect in vibrational spectra of the MnF3 molecule

The experimental data on the structure and vibrational spectrum of the MnF₃ molecule are analyzed. The vibrational modes are calculated and the vibrational spectrum of MnF₃ is interpreted. A model of the electronic structure of trifluorides of transition metals is suggested which explains the observation of the strong Jahn-Teller effect in MnF₃, and the influence of this effect on the molecular spectrum is discussed.     

Formation of electronically excited states in ultrathin Alq3 films during electron bombardment

Electronic and vibrational electron energy loss spectra are studied on ultrathin Alq₃ films for different electron energies, thicknesses, and temperatures of the film. The shape of the spectrum and the position of the lines are very weakly dependent on the film thickness, indicating weak interaction between the adsorbed molecules and the platinum substrate. The temperature dependence of the vibrational bands is weak. The positions of the triplet and singlet maxima are close to gas-phase and thin-film data obtained for high electron energy. Interference of electrons is observed in measuring the energy loss spectra. The effect of dipole and collisional excitation mechanisms is shown. From the similarity between the energy loss spectra it follows that the nature of the interaction between low-energy electrons and organic materials is the same in gas and thin-film phases, and likewise for the characteristics of the motion of the electrons. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 786–791, November–December, 2006.     

Strain induced phase separation on La0.5Ca0.5MnO3 thin films

The effect of epitaxial strain on La_0.5Ca_0.5MnO₃ films of various thicknesses grown on SrTiO₃, SrLaAlO₄, and SrLaGaO₄ substrates is studied by Raman spectroscopy, magnetic, and resistivity measurements. The transport and magnetic properties as well as Raman spectra of the films are affected by epitaxial strains. The energy of the A_g(2) mode and the tilting angle of the MnO₆ octahedra is affected by the strain imposed by the substrate. In the spectra of the films deposited on the (1 0 0) SrTiO₃ substrate strong Jahn-Teller (JT) modes appear, which couple with charge-ordering. In all other films these modes are suppressed and no additional Raman lines are present at low temperatures contrary to the bulk compound. The low frequency continuum scattering decreases at low temperatures indicating a coupling with both the charge and orbital transitions. Comparison of the Raman spectra with the magneto-transport properties suggests an interpretation in terms of a strain induced phase separation between ferromagnetic metallic and antiferromagnetic insulating states.     

Relationships among Jahn-Teller reduction factors for a Γ8 state in cubic symmetry

The general form of the reduction factors for a fourfold degenerate Γ₈ state in cubic symmetry is obtained for linear Jahn-Teller coupling to one or more vibrational modes of E(Γ₃) and/or T₂(Γ₅) symmetry.     

Spectroscopic effects of conical intersections of molecular potential energy surfaces

A simple vibronic coupling model involving two electronic states and two vibrational modes is considered. The model is based on harmonic diabatic potentials and linear coupling of the diabatic electronic states. It is shown that the adiabatic electronic potential energy surfaces exhibit, in general, a conical intersection. The well known E × E and E × B Jahn-Teller problems are contained as special cases. Using numerical methods the optical absorption spectrum is calculated exactly. Extremely complex vibronic spectra are obtained when the conical intersection occurs within the Franck-Condon (FC) zone. The exact vibronic spectra are compared with spectra calculated in the adiabatic and FC approximation. The genuine spectroscopic effects of conical intersections are revealed by a comparison with the results of standard one-dimensional vibronic coupling calculations. The presence of a conical intersection limits the applicability of the adiabatic and FC approximations much more strongly than in the one-dimensional case. The upper adiabatic electronic state is strongly affected by non-adiabatic coupling even when the point of intersection lies outside the FC zone. The relevance of these results for the calculation of molecular electronic spectra is briefly discussed.     

Resonance photoconductivity in Fe-doped InP

A photoconductivity peak at 0.44 eV is observed in Fe-doped InP. This peak is attributed to electrons which are optically excited from the Fe²⁺⁵E ground state to vibronic levels of the ⁵T₂ excited state, and thermally excited from there to the conduction band. The lineshape is nearly Gaussian and is well fitted by assuming a vibronic coupling energy of about 0.06 eV in the ⁵T₂ state. In analogy with results in the II–VI compounds this coupling may be dominated by interaction with non-symmetric lattice modes which produce a dynamic Jahn-Teller effect.     

Large quadratic interaction for the coexistence of two kinds of Jahn-Teller distortions in KI:T1-type phosphors

A modified Fukuda model, which is based on the coexistence of T¹ tetragonal and X rhombic minima on the ³T¹_1u energy levels due to Jahn-Teller effect, is tested by means of the available experimental data concerning absorption and emission bands positions and the electron-lattice coupling constant for E_g modes. The model is satisfactory only if a strong difference in curvature between the ground and excited levels $\text{(β ? 0.75)}$ is assumed; this suggests that second order Jahn-Teller effect terms may be important.     

Effects of vibrational intercentre interaction in a trigonal two-centre system with twofold electronic degeneracy at each centre

The effect of intercentre interaction (via vibrations and electron-electron coupling) on the magnetic and magnetic resonance characteristics of a pair of Jahn-Teller centres is investigated. In the limiting case of strong vibronic coupling when the splitting of degenerate electronic terms is sufficiently large the exchange Hamiltonian for the pair has the Heisenberg form. The energy spectrum of spin states of the pair system is obtained and the temperature dependence of the effective magnetic moment is investigated. It is shown that under some conditions this temperature dependence has an anomalous nonmonotonic character. The g factors of the two-centre Jahn-Teller system are obtained and the changes of the EPR spectrum with the exchange and vibrational coupling constants is analysed. With inclusion of only the exchange interaction, the pair spectrum possesses an additional isotropic resonance placed in the middle of the known broadened EPR spectrum of single centres with the Jahn-Teller effect for an orbital E term. The vibrational interaction between the centres results in a radical transformation of the spectrum, which in this case contains only an isotropic resonance line.     

The Influence of Temperature on Coumarin 153 Fluorescence Kinetics

The influence of temperature varied in the range 183 K–323 K on the fluorescence quantum yield, fluorescence lifetime, absorption and emission transition moments and non-radiative deactivation rate was determined for the well known and largely used dye Coumarin 153, dissolved in 1-chloropropane. The Kennard-Stepanov relation connecting the absorption and emission spectra was used to check for the presence of more than one absorbing/emitting species and to investigate whether intramolecular vibrational redistribution completes in the C153 excited S ₁ state before the emission takes place. The emission spectrum corresponding to S ₁→S ₀ transition, was fitted at each temperature to the model function including the information on the dye vibrational modes coupling. In this way the displacement in equilibrium distance for the most active vibrational mode was determined for C153 in S ₁ and in S ₀. Using the temperature dependence of the fluorescence decay time and quantum yield, the non-radiative deactivation rate was determined. Its temperature dependence was compared to that calculated using the theoretical model with the most active vibrational mode displacement values taken from steady-state spectra analysis. The somewhat surprising dependence of the fluorescence decay time and quantum yield on temperature was related to non-trivial coupling between low-frequency vibrational modes of C153 in the excited and ground states.