H2O和HLi分子的双光子激发

用全相对论量子力学计算H2O和HLi的双光子偶极激发。为对比起见,同时用非相对论的对称匹配团族-组态相互作用法(SAC-CI)计算其单光子激发。对于无对称中心的H2O和HLi,符合相应群的对称选择原则。双光子跃迁几率一般比单光子跃迁的小3～5个数量级。在计算双光子偶极激发时,应采用同时包含了空间的对称性和时间反转对称性的全相对论。     

分子XH(X=O,S, Se和 Te)中的正电子能级与正电子原子

基于全对称群的Dirac方程, 研究当存在核场时的正电子能级及其与核场的关系, 即计算在分子OH, SH, SeH和 TeH的核场下的正电子能级. 这时正电子的能量约为 e⁺=-1.022 MeV. 对于低能级, 当核场强增大时, 其能量有所升高, 而对较高能级, 核场强增大时, 其能量无明显变化. 正负电子的湮没过程为三光子湮没过程(the three-photon annihilation). 而当生成e⁺- e^-< 关键词： Dirac方程 三光子湮没过程 正态的正电子原子 电荷宇称守衡     

类锂离子(Z=3～100)磁偶和电偶的跃迁几率和能级间隔的相对论计算

采用全相对论多组态Dirac-Fock方法，分别计算了类锂离子（Z＝3－100)的磁偶跃迁1s^23s^2S1/2→1s^22s^2S1/2和电偶跃迁1s^2p^2P1/2→1s^22s^2S1/2的能级间隔，QED贡献和跃迁几率，比较了两者的参数与核电荷数Z的关系的差异，认为原子序数很大时，磁偶跃迁几率不能忽视。     

类铍离子磁四极M2 2s2 1S0—2s2p3P2 (Z=10—103)禁戒跃迁

利用全相对论多组态Dirac-Fock方法系统地计算了高离化类铍离子的磁四极M2 2s²¹S₀—2s2p³P₂ (Z=10—103)自旋禁戒跃迁的能级间隔、跃迁概率和振子强度，计算中考虑了重要核的有限体积效应，Breit修正和QED修正，所得结果和最近的实验数据以及理论值进行了比较，结果表明：高原子序数的高电荷离子(Z≥70)磁四极M2自旋禁戒跃迁几乎可以和中性原子的光学允许跃迁相比拟，不仅在天体等离子体中，在ICF和MCF高温激光等离子体中，磁四极自旋禁戒跃迁和其他自旋禁戒跃迁（磁偶极、电四极）一样不容忽视，在双电子复合、不透明度、自由程等理论计算中应该考虑其影响. 关键词： 磁四极M2 能级间隔 跃迁概率 振子强度     

LiGaX2(X=S,Se, Te)的电子结构,光学和弹性性质的第一性原理计算

采用基于第一性原理的密度泛函理论赝势平面波方法,对LiGaX₂(X=S, Se, Te)的能带结构、态密度、光学以及弹性性质进行了理论计算. 能带结构计算表明LiGaS₂ 的禁带宽度为4.146 eV, LiGaSe₂ 的禁带宽度为3.301 eV, LiGaTe₂ 的禁带宽度为2.306 eV; 其价带主要由Ga-4p 层电子和X- np 层电子的能态密度决定; 同时也对LiGaX< 关键词： 电子结构 光学性质 弹性性质 LGX     

双光子激发NO分子里德伯态H~(''''2)Ⅱ~-的光谱研究

本文采用激光双光子激发的方法对NO分子的里德伯态H~(12)Ⅱ-(v=1,2)进行了研究,得到了该能级的光谱常数;观测到了H~(12)Ⅱ-与非里德伯态B~2Ⅱ之间的相互作用现象,并计算出了相应的转动能级位移;研究了H~(12)Ⅱ-能级的主要荧光跃迁通道。     

高离化Kr33+离子22P -n2S(2≤n≤9)的耦极跃迁行为

本文构造了高离化Kr33+离子 1s2ns (2≤n≤9)和1s22p 态的波函数并利用其计算了体系的非相对论能量。为了得到高精度的理论计算结果,将相对论修正和质量极化效应作为一级微扰计算了体系的总能量和22P -n2S(2≤n≤9)跃迁能,本文的结果与有限的实验数据符合的较好。在此基础上完成了22P -n2S(2≤n≤9)偶极跃迁三种规范下振子强度的理论计算,三者的一致性进一步证明所构造的波函数在整个空间的准确性和可靠性。     

LiBX2 (B=Ga, In; X= S, Se, Te)光学性质与力学性质的第一性原理计算

采用基于第一性原理的赝势平面波方法系统地计算了LiBX₂ (B= Ga, In; X= S,Se,Te) 晶体的光学性质与力学性质. 由禁带宽度推断出晶体抗激光损伤阈值的大小顺序为LiGaS₂ > LiInS₂ > LiGaSe₂ > LiInSe₂ > LiGaTe₂ > LiInTe₂. 六种晶体在常压下均满足机械力学稳定性要求, 且铟化合物可塑性及延展性强于镓化合物. 这些晶体的静态电介电常数 ε₁(0)、静态折射率n(0)和双折射率Δn 理论计算值与实验值相符. LiGaS₂, LiInS₂, LiGaSe₂, LiInSe₂和LiGaTe₂五种化合物双折射率较高, 并且它们的吸收谱与反射谱在中远红外区是透过的, 因此可推断出这五种化合物可以成为优异的中远红外非线性光学材料.     

Al2O3X(X=H,D, T)的电子振动近似理论方法研究

用密度泛函理论(DFT)方法在6-311++G(d,p)水平上对Al₂O₃X(X=H, D, T)分子较低能量的几何构型进行了优化. 计算结果表明该分子有两个可能基态, 即Al₂O₃X(X=H,D,T)(²A′)C_s和Al₂O₃X 关键词： 2O₃X(X=H;D;T)分子团簇')" href="#">Al₂O₃X(X=H;D;T)分子团簇 热力学函数 氢同位素效应 吉布斯自由能改变     

~(39)K_2分子C~1Ⅱ_u-X~1∑_9~+(J′=105)Q支激光诱导荧光光谱及电偶极跃迁矩变化率研究

用4415.6(?)CW激光线获得了~(39)K_2分子C~1II_u(v′=0,J′=105)-X~1∑_g~+(v″=1～10,J″=105)Q支激光诱导荧光(LIF)光谱.用最小二乘法拟合出了~(39)K_2分子X~1∑_g~+态振动常数和C~1II_u态电子谱项值T_e.光谱分析表明C~1II_u态T_e=22968cm~(-1)是合适的.用~(39)K_2分子Morse势计算了(V′=0,J′=105)-(v″=1～10,J″=105)跃迁的Franck-Condon因子和跃迁强度,强度计算值和激光诱导荧光光谱测量值之间有令人满意的符合,进一步的r重心近似分析给出了~(39)K_2分子C~1II_u→X~1∑_g~+电偶极跃迁矩R_(?)随核间距r的归一化变化率为-0.157～-0.168 debye/(?)(4.22(?)相似文献   

Molecular Structures of H2X and D2X(X=0, S,Se, Te)

There are two possible configurations for H₂O, linear(D_∞h) or bent(C_2v). For a C_2v′, the three bands ν_1′ ν₂ and ν₃ should appear in both Raman and infrared. For a D_∞h. however, the ν₁, band should appear in only Raman and the ν₂ and ν₃ bands, in only infrared, that is, a principle of mutual exclusion of Raman and infrared should hold. The present author concludes that H₂X and D₂X(X=O, S, Se, Te) have a linear D_∞h. structure, since the obtained spectra show mutual exclusion of Raman and infrared.     

Structural and elastic properties of barium chalcogenides (BaX,X=O,Se, Te) under high pressure

In the present paper we have investigated the high-pressure, structural phase transition of Barium chalcogenides (BaO, BaSe and BaTe) using a three-body interaction potential (MTBIP) approach, modified by incorporating covalency effects. Phase transition pressures are associated with a sudden collapse in volume. The phase transition pressures and associated volume collapses obtained from TBIP show a reasonably good agreement with experimental data. Here, the transition pressure, NaCl-CsCl structure increases with decreasing cation-to-anion radii ratio. In addition, the elastic constants and their combinations with pressure are also reported. It is found that TBP incorporating a covalency effect may predict the phase transition pressure, the elastic constants and the pressure derivatives of other chalcogenides as well.      

Electronic properties of chalcopyrite CuAlX2(X=S,Se,Te) compounds

We present results of the band structure and density of states for the chalcopyrite compounds CuAlX₂ (X=S,Se,Te) using the state-of-the-art full potential linear augmented plane wave (FP-LAPW) method. Our calculations show that these compounds are direct band gap semiconductors. The energy gap decreases when S is replaced by Se and Se replaced by Te in agreement with the experimental data. The values of our calculated energy gaps are closer to the experimental data than the previous calculations. The electronic structure of the upper valence band is dominated by the Cu-d and X-p interactions. The existence of Cu-d states in the upper valence band has significant effect on the optical band gap.     

A Raman study of high-pressure phases of lead chalcogenides PbX (X=S,Se, Te)

Pressure-induced phase transitions of lead chalcogenides were studied by Raman spectroscopy. The number of Raman modes observed for the first high-pressure phases was found to be significantly less than expected from selection rules for the proposed GeS-type orthorhombic structure. The observations are consistent with the alternative assignment as CrB-type. In the case of PbS, the disappearance of the intermediate-phase Raman lines in the pressure range of 19–25 GPa, i.e., in the vicinity of the orthorhombic to CsCl-type phase transition, is accompanied by a strong increase in a structureless background. The Raman background is attributed to light scattering by charge carriers in the metallic CsCl-type phase.     

Full relativistic calculations of the quadrupole and electric field gradients for C2, N2, and O2

In the present work we calculate the energies,quadrupole moments,and electric field gradients(EFGs) of molecules C2,N2,and O2 based on the DIRRCI method with basis aug-cc-pVTZ-DK.We prove that the quadratic force constant k2 is the product of charge and EFG at its equilibrium nuclear distance.The dipole charge distributions for these symmetrical molecules are all in equilibrium,however,the quadrupole charge distributions are far from equilibrium;among these,there is the most remarkable deviation from equilibrium for N2,for its many charges concentrate on two sides of the molecule,which is in agreement with the well-known characteristic of the nitrogen molecule.The relativistic effect is remarkable even for the same period.     

(ZnX)_3(X=S、Se和Te)量子点配体效应的密度泛函理论研究

采用密度泛函理论研究了一系列含磷配体(OPH_3、OPH_2Me、OPHMe_2和OPMe_3)对量子点(ZnX)_3(X=S、Se、Te)结构和性质的影响.Zn原子与配体中的O原子生成新的Zn-O配位键,使量子点的结构、吸附能、电荷分布、吸收光谱和HOMO-LUMO轨道等性质随着配体中甲基数目逐渐增多发生规律性的改变.计算结果表明:有机配体三甲基氧膦(OPMe_3)是阻止小尺寸(ZnX)_3量子点聚集,保护此类量子点的较为有效的配体.     

高压下钡的硫化物的结构相变和光学性质研究(英文)

利用基于密度泛函的第一性原理,计算了高压下钡的硫化物(BaS、BaSe和BaTe)的结构相变和光学性质。计算结果表明,这些化合物的压致结构相变是从NaCl型结构转变为CsCl型结构;对于结构转变压力和金属化转变压力,BaS为8.57 GPa和45.4 GPa,BaSe为7.44 GPa和36.5 GPa,BaTe则分别为5.67 GPa和16.7 GPa。光学性质计算结果显示:随着压力的增加,静态介电常数ε0不断增加,介电常数虚部ε2的峰值向高能方向移动(蓝移)。     

Resonance photoelectron spectroscopy of TiX2 (X = S, Se, Te) titanium dichalcogenides

The photoelectron valence band spectra of TiS₂, TiSe₂, and TiTe₂ dichalcogenides are investigated in the Ti 2p-3d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS₂ and TiTe₂. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS₂, TiSe₂, and TiTe₂ compounds intercalated by titanium atoms. Analysis of experimental data and their comparison with model calculations showed that these bands have different origins. It is found that the resonance enhancement of an additional band observed in TiS₂ is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe₂ is caused by occupation of the 3d band in Ti.     

分子H_2X(X=O、S、Se)的全对称群Dirac理论研究

本文应用全对称群的Dirac理论计算了分子H_2X(X=O、S、Se)的结构,并与非相对论的结果比较.对比相对论和非相对论的结果,所得到的分子几何差异不大;而所计算的能量,相对论的比非相对论的要低,并能量随质量增加而降低;相对论值的极化率(A~3)和偶极矩更接近实验值.分子的电性状态为费密子共群的不可约表示E_1,明显地体现不可约表示E1的效应.所以,特别对重元素分子,更要应用相对论方法.     

Many-body effects on the width of the band gap in Bi2Te2X (X = Te, Se, S) topological insulators

The spectrum of quasiparticles of Bi₂Te₂X (X = Te, Se, S) three-dimensional topological insulators has been theoretically studied in the GW approximation with the inclusion of the spin-orbit interaction in the construction of the Green’s function and self-energy. It has been shown that many-body corrections to the Kohn-Sham states in Bi₂Te₂X increase the fundamental band gap similar to conventional semiconductors. However, the band gap at the Γ point decreases in this case. Gaps in the quasiparticle spectrum obtained in agreement with the experimental data correspond to the difference between the minimum of the conduction band, which is located on the Γ-Z line, and the maximum of the valence band, which lies beyond the symmetric directions in the mirror plane.