两种新型芴衍生物的合成、晶体结构及光谱性能

合成了两种新型芴衍生物:2,7-二（3,5-二（三氟甲基）苯基）-9,9-二乙基芴（1）和2,7-二（4-氟苯基）-9,9-二乙基芴（2）。通过元素分析、红外光谱（IR）、核磁共振氢谱（¹H NMR）以及单晶X射线衍射对其结构进行了表征。化合物1属于单斜晶系,P2₁/c空间群;化合物2属于三斜晶系,P-1空间群。通过紫外-可见吸收和荧光光谱研究了化合物的发光性能。结果表明:在CH₂Cl₂溶液和固态薄膜中,化合物1、2在350～400 nm波段有吸收峰,归属于π-π^*电荷跃迁;化合物1、2的光学带隙E_g分别为3.31 eV和3.30 eV,并且均有强烈的蓝色荧光发射现象（激发波长为330 nm）,在二氯甲烷中的荧光量子效率分别为0.62和0.61,固态荧光寿命分别为6.39 ns和9.00 ns。     

Equilibrium dynamics of the sub-Ohmic spin-boson model under bias

Using the bosonic numerical renormalization group method, we studied the equilibrium dynamical correlation function C(ω) of the spin operator σ_z for the biased sub-Ohmic spin-boson model. The small-ω behavior C(ω) ∝ω~s is found to be universal and independent of the bias ε and the coupling strength α(except at the quantum critical point α = αc and ε = 0). Our NRG data also show C(ω) ∝χ~2ω~s for a wide range of parameters, including the biased strong coupling regime(ε = 0 and α α_c), supporting the general validity of the Shiba relation. Close to the quantum critical point αc,the dependence of C(ω) on α and ε is understood in terms of the competition between ε and the crossover energy scale ω_0~*of the unbiased case. C(ω) is stable with respect to ε for ε《ε~*. For ε》ε~*, it is suppressed by ε in the low frequency regime. We establish that ε~*∝(ω_0~*)~(1/θ)holds for all sub-Ohmic regime 0≤s 1, with θ = 2/(3s) for 0 s≤1/2 and θ = 2/(1 + s) for 1/2 s 1. The variation of C(ω) with α and ε is summarized into a crossover phase diagram on the α–ε plane.     

The charge neutrality level and the fermi level pinning in A<Superscript>3</Superscript>N (BN,AlN, GaN,InN) nitrides

The electronic band structure and position of the charge neutrality level (CNL) in BN, AlN, GaN, and InN compounds with cubic and hexagonal lattices are calculated within the density functional theory (DFT-GGA). It is shown that the charge neutrality level is shifted from the middle of the BN and AlN forbidden band to the upper half of the GaN forbidden band and to the allowed energy region in the InN conduction band as the cation atomic weight increases. This determines semiinsulating properties of BN and AlN, n-type conductivity of GaN, and n ⁺-type conductivity of InN upon saturation of these materials by intrinsic lattice defects due to hard radiation. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 24–31, December, 2008.     

Nonlinear Response of Granular Composite Mediurn

In this paper, the linear and nonlinear responses of granular composite medium consisting of spherical grains with coating shells embedded in a host medium are studied. We assume that the shell and the host medium are linear (the dielectric constants of which are ε⁰ and ε_m⁰ respectively), while the spherical grain is nonlinear (the diektric constant of which is ε_c = ε_c⁰ + χ_c|E_c|^β). Starting from the definition (D) = ε_eff and taking in to account the corrections to the local field within the spherical grains, expressions for the linear and high-order nonlinear susceptibilities are presented.     

Mechanical,elastic, anisotropy,and electronic properties of monoclinic phase of m-Si_xGe_(3-x)N_4

The structural,mechanical,elastic anisotropic,and electronic properties of the monoclinic phase of m-Si_3N_4,mSi_2GeN_4,m-SiGe_2N_4,and m-Ge_3N_4are systematically investigated in this work.The calculated results of lattice parameters,elastic constants and elastic moduli of m-Si_3N_4and m-Ge_3N_4are in good agreement with previous theoretical results.Using the Voigt–Reuss–Hill method,elastic properties such as bulk modulus B and shear modulus G are investigated.The calculated ratio of B/G and Poisson’s ratio v show that only m-SiGe_2N_4should belong to a ductile material in nature.In addition,m-SiGe_2N_4possesses the largest anisotropic shear modulus,Young’s modulus,Poisson’s ratio,and percentage of elastic anisotropies for bulk modulus ABand shear modulus AG,and universal anisotropic index AUamong m-Si_xGe_(3-x)N_4(x=0,1,2,3.)The results of electronic band gap reveal that m-Si_3N_4,m-Si_2GeN_4,m-SiGe_2N_4,and m-Ge_3N_4 are all direct and wide band gap semiconducting materials.     

Ge-As-S硫系玻璃的结构与性能调控

制备了系列具有不同化学配比特征的Ge-As-S硫系玻璃,并研究了玻璃的结构、折射率和光学带隙(Eg).Ge-As-S玻璃具有以[Ge S_4]四面体和[As S_3]三角锥为骨架结构单元相互交联形成的连续网络结构,当S过量时,结构中出现S链或S_8环;当S不足时,结构中形成As_4S_4/As_4S_3分子,甚至出现大量AsAs/Ge-Ge同极键.玻璃的组成元素在2—10μm波段的摩尔折射度分别为R_(Ge)=9.83—10.42 cm~3/mol,RAs=11.72—11.87 cm~3/mol和R_S=7.78—7.86 cm3/mol.Ge-As-S玻璃的折射率与密度和组成元素的摩尔折射度之间存在较好的定量关系,可根据该定量关系在1%偏差内对玻璃的折射率进行预测或调控.提出了采用玻璃粉末的漫反射光谱确定可靠Eg的方法,通过该方法可获得玻璃的强吸收数据用于确定Eg.Ge-As-S玻璃的Eg与玻璃的平均键能之间存在较好的关联,S含量较高的玻璃更倾向于具有较大的平均键能,因此具有较大的Eg.     

First-principles analysis of the structural,electronic, and elastic properties of cubic organic-inorganic perovskite HC(NH_2)_2PbI_3

The structural, electronic, and elastic properties of cubic HC(NH_2)_2PbI_3 perovskite are investigated by density functional theory using the Tkatchenko–Scheffler pairwise dispersion scheme. Our relaxed lattice parameters are in agreement with experimental data. The hydrogen bonding between NH_2 and I ions is found to have a crucial role in FAPbI_3 stability. The first calculated band structure shows that HC(NH_2)_2PbI_3 has a direct bandgap(1.02 eV) at R-point, lower than the bandgap(1.53 eV) of CH_3NH_3PbI_3. The calculated density of states reveals that the strong hybridization of s(Pb)–p(I) orbital in valence band maximum plays an important role in the structural stability. The photo-generated effective electron mass and hole mass at R-point along the R–Γ and R–M directions are estimated to be smaller: m_e~*= 0.06 m0 and m_h~*= 0.08 m0 respectively, which are consistent with the values experimentally observed from long range photocarrier transport. The elastic properties are also investigated for the first time, which shows that HC(NH_2)_2PbI_3 is mechanically stable and ductile and has weaker strength of the average chemical bond. This work sheds light on the understanding of applications of HC(NH_2)_2PbI_3 as the perovskite in a planar-heterojunction solar cell light absorber fabricated on flexible polymer substrates.     

Cu,Fe掺杂LiNbO_3晶体电子结构和光学性质的第一性原理研究

利用基于密度泛函理论的第一性原理对Cu,Fe单掺及共掺LiNbO_3晶体的电子结构和光学性质进行了计算.结果显示:Cu,Fe单掺杂LiNbO_3晶体禁带内均产生了杂质能级,主要由Cu3d,Fe3d轨道及O 2p轨道贡献;共掺LiNbO_3晶体禁带内出现了双能级结构,深能级由Cu3d和O2p轨道贡献,浅能级由Fe3d和O2p轨道贡献.Cu,Fe单掺和共掺LiNbO_3晶体带隙依次缩小,在可见光区的光吸收明显增强.共掺LiNbO_3在445和630nm左右分别表现出一个宽吸收峰,比单掺LiNbO_3晶体表现出更好的光吸收性质.研究表明,Fe占Nb位比Fe占Li位的双掺样品在双光存储应用中更有优势;同时,浓度比[Fe2+]/[Fe3+]值的适当降低有助于这种优势的形成.     

An Improved Study of Electronic Band Structure and Optical Parameters of X-Phosphides (X=B,Al, Ga,In) by Modified Becke-Johnson Potential

We report the electronic band structure and optical parameters of X-Phosphides (X=B, Al, Ga, In) by first-principles technique based on a new approximation known as modified Becke-Johnson (mBJ). This potential is considered more accurate in elaborating excited states properties of insulators and semiconductors as compared to LDA and GGA. The present calculated band gaps values of BP, AlP, GaP, and InP are 1.867 eV, 2.268 eV, 2.090 eV, and 1.377 eV respectively, which are in close agreement to the experimental results. The band gap values trend in this study is as: E_g(mBJ-GGA/LDA) > E_g(GGA) > E_g(LDA). Optical parametric quantities (dielectric constant, refractive index, reflectivity and optical conductivity) which based on the band structure are also presented and discussed. BP, AlP, GaP, and InP have strong absorption in between the energy range 4-9 eV, 4-7 eV, 3-7 eV, and 2-7 eV respectively. Static dielectric constant, static refractive index and coefficient of reflectivity at zero frequency, within mBJ-GGA, are also calculated. BP, AlP, GaP, and InP show significant optical conductivity in the range 5.2-10 eV, 4.3-8 eV, 3.5-7.2 eV, and 3.2-8 eV respectively. The present study endorses that the said compounds can be used in opto-electronic applications, for different energy ranges.     

高压下NH_4ClO_4结构、电子及弹性性质的第一性原理研究

研究高压下NH_4ClO_4的结构和性质对于NH_4ClO_4在固体推进剂和炸药的安全应用具有重要意义.采用基于色散校正密度泛函理论的第一性原理方法,研究了0—15 GPa静水压力下NH_4ClO_4的晶体结构、分子结构、电子性质和弹性性质,计算结果与实验值具有较好的一致性.在压强为1,4和9 GPa时,NH_4ClO_4的晶体参数、键长和分子构型等均出现不连续变化,说明了在压强作用下结构发生变化.随着压强增加,氢键增多且作用增强,由分子内氢键向分子内和分子间的氢键转变;导带态密度峰值增加,电子局域性增强,晶体内N-H和Cl-O共价键作用增强,带隙增大,不同相变区域内带隙呈线性关系.0—15 GPa条件下NH_4ClO_4的弹性常数满足力学稳定性标准,采用Voigt-Reuss-Hill方法计算了体积模量B,剪切模量G和杨氏模量E,根据Cauchy压力和B/G值,说明NH_4ClO_4属于韧性材料,随着压强增加韧性增强.     

富勒烯C20四聚体的结构与性能研究

采用密度泛函理论(DFT)中的杂化密度泛函(B3LYP)方法, 在6-31 G基组水平上对C₂₀四聚体进行了几何参数全优化, 得到了基态构型, 并对其稳定性、电子结构、极化率和芳香性进行了计算研究. 结果表明: C₂₀碳笼以[2+2]加成方式结合形成C₂₀四聚体, 具有良好的热力学稳定性; C原子内部以sp²的方式杂化, C原子之间有少量电荷转移; C₂₀ 四聚体的IR和Raman光谱都有较多的振动峰; 随碳笼数的增加, C₂₀聚合物中原子间的成键相互作用随之增强; C₂₀四聚体具有芳香性.     

First-principles Study on the Magnetic,Half-metal and Thermoelectric Transport Properties of Inorganic-Organic Hybrid Compounds [C4N2H12][Fe4Ⅲ(HPO3)2(C2O4)3]

The electronic structure, magnetic and half-metal properties of inorganic-organic hybrid compound [C₄N₂H₁₂][Fe₄^Ⅲ(HPO₃)₂(C₂O₄)₃] are investigated by using the full-potential linearized augmented plane wave (FPLAPW) method within density-functional theory (DFT) calculations. The density of states (DOS), the total energy of the cell and the spontaneous magnetic moment of [C₄N₂H₁₂][Fe₄^Ⅱ(HPO₃)₂(C₂O₄)₃] are calculated. The calculation results reveal that the low-temperature phase of [C₄N₂H₁₂][Fe₄^Ⅲ(HPO₃)₂(C₂O₄)₃] exhibits a stable ferromagnetic (FM) ground state, and we find that this organic compound is a half-metal in FM state. In addition, we have calculated antiferromagnetically coupled interactions, revealing the existence of antiferromagnetic (AFM), which is in agreement with the experiment. We have also found that [C₄N₂H₁₂][Fe₄^Ⅲ(HPO₃)₂(C₂O₄)₃] is a semiconductor in the AFM state with a band gap of about 0.40 eV. Subsequently, the transport properties for potential thermoelectric applications have been studied in detail based on the Boltzmann transport theory.     

Effect of LO-Phonons on the Hydrogenic Impurities in a Spherical Quantum Dot

By applying the method of variational wavefunction and adopting the approximation of 3D-Frohlich Hamiltonian for electron-LO phonon interaction in a spherical quantum dot (SQD), we have calculated the ground-state energy E, and binding energy E_g of a bound polaron confined in a GaAs/Ga_χAl_1-χSQD. These energies vary as the value of the boundary potential of the SQD and the deviation of the position of the hydrogenic impurity from the centre of the sphere. In this system of concern, R = 2a^*, a^* is the effective Bohr radius, is an appropriate criterion for the radius R of an SQD when the effect of quantum confinement has to be considered.     

InOOH压致氢键对称化及其弹性性质

利用第一性原理研究了InOOH在高压下的氢键对称化行为及其对InOOH弹性等性质的影响.结果表明约在18 GPa时InOOH中的氢键发生了对称化转变,导致轴比率b/c对压力的斜率由负值变为正值;压缩弹性常数、非对角弹性常数、体积模量和纵波波速出现异常增加,如体积模量增加了20%—40%.高压下InOOH弹性性质呈现出更加明显的各向异性.常压下InOOH呈现韧性,且伴随着氢键对称化韧性异常增加.对畸变金红石型MOOH(M=Al,In,Ga,Fe,Cr)化合物在高压下的弹性性质转变与氢键性质转变的耦合规律进行了初探.     

Electrical conductivity, optical and metal–semiconductor contact properties of organic semiconductor based on MEH-PPV/fullerene blend

The electrical conductivity, optical and metal–semiconductor contact properties of the MEH-PPV:C₇₀ organic semiconductor have been investigated. The electrical conductivity results show that the MEH-PPV:C₇₀ film is an organic semiconductor. The optical band gap of the film was found to be 2.06 eV and the fundamental absorption edge in the film is formed by the direct allowed transitions. The refractive index dispersion curve of the film obeys the single oscillator model and E_d and E_o dispersion parameters were found to be 10.61 and 3.89 eV, respectively. The electrical characterization of the ITO/MEH-PPV:C₇₀ diode have been investigated by current–voltage characteristics. ITO/MEH-PPV:C₇₀ diode indicates a non-ideal current–voltage behavior with ideality factor n (2.50) and barrier height φ_B (0.90 eV) values.     

ZrV2结构、弹性和热力学性质的第一性原理计算

采用基于密度泛函理论的第一性原理平面波赝势方法研究ZrV₂的晶体结构和弹性,利用准谐Debye模型计算在不同温度(T=0~1200 K)和不同压强(P=0~20 GPa)下ZrV₂的热力学性质,包括弹性模量与压强,热熔与温度,以及热膨胀系数与温度和压力的关系.结果表明:计算的ZrV₂晶格常数与实验值符合较好,晶体材料的弹性常数随着压力增加而增加;在一定温度下,相对体积、热熔随着压强的增加而减小,德拜温度、弹性模量随着压强的增加而增加,且高压下温度对ZrV₂热膨胀系数的影响小于压强的影响.     

高压下Ti_2AlX(X=C,N)的结构、力学性能及热力学性质

采用基于密度泛函理论的第一性原理方法,计算研究了压力对Ti_2AlC与Ti_2AlN结构、力学性能的影响.研究发现压力的增大会使体系的体积比降低,Ti_2AlC压缩性较Ti_2AlN好.力学性能研究发现,压力的增大使材料抵抗变形能力增强,体系的延展性有了很大的提升,当压力超过40 GPa后,Ti_2AlC与Ti_2AlN从脆性材料转变为延性材料,体模量与剪切模量的比值达到1.75,延展性有了很大的提升.通过准谐德拜模型,分析了压力与温度对Ti_2AlC与Ti_2AlN体模量、热容及热膨胀系数的影响.结果表明,随着温度的升高,Ti_2AlN与Ti_2AlC的体模量下降.定容热容与定压热容的变化趋势相同,但在高温下,定容热容遵循Dulong-Petit极限,温度对热容的影响效果较压力明显.温度与压力对Ti_2AlN与Ti_2AlC线膨胀系数的影响主要发生在低温区域.     

First-Principles Calculations of Structural,Elastic and ElectronicProperties of Tetragonal HfO2under Pressure

Structural, elastic and electronic properties of tetragonal HfO₂ at applied hydrostatic pressure up to 50 GPa have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The calculated ground-state properties are in good agreement with previous theoretical and experimental data. Six independent elastic constants of tetragonal HfO₂ have been calculated at zero pressure and high pressure. From the obtained elastic constants, the bulk, shear and Young's modulus, Poisson's coefficients, acoustic velocity and Debye temperature have been calculated at the applied pressure. Band structure shows that tetragonal HfO₂ is an indirect band gap. The variation of the gap versus pressure is well fitted to a quadratic function.     

CHClF2在强红外激光作用下C2*d3Пg态的形成机制

用TEACO₂激光辐照CHCIF₂分子生成电子激发态C₂^*自由基,观察到斯旺带系的六个谱带。本文根据C₂分子态位能曲线的特点,提出C₂^*d³Π_g态的形成机制。C₂是少数较特殊的分子之一,其激发态b³Σ_g^-与第一激发态a关键词：     

P213 BN: a novel large-cell boron nitride polymorph

A new boron nitride polymorph, P2₁3 BN (space group: P2₁3), is investigated by first-principles calculations, including its structural properties, stability, elastic properties, anisotropy and electronic properties. It is found that the new boron nitride polymorph P2₁3 BN is mechanically, dynamically and thermodynamically stable. The bulk modulus (B), shear modulus (G) and Young's modulus of P2₁3 BN are 91 GPa, 41 GPa and 107 GPa, respectively, all of which are larger than that of Y carbon and TY carbon. By comparing with c-BN, the Young's modulus, shear modulus and Poisson's ratio of P2₁3 BN show tiny anisotropy in the (001), (010), (100) and (111) planes. At the same time, in contrast with most boron nitride polymorphs, P2₁3 BN is a semiconductor material with a smaller band gap of 1.826 eV. The Debye temperature and the anisotropic sound velocities of P2₁3 BN are also investigated in this work.