Si3Xn (X=C,O,N;n=1,2)团簇的密度泛函研究

使用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对Si3Xn(X=C,O,N;n=1,2)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的电子结构、振动特性、成键特性和电荷特性等进行了理论研究.结果表明团簇的几何结构都是平面结构,通常Si3X2出现是Si-X键,较少出现X-X键;而Si3X中出现Si-X键和Si-Si键共存,Si3Xn(X=C,O,N;n=1,2)团簇的电荷布局分布表明这种电荷转移的作用使得团簇中所有X原子呈负电性,Si原子显正电性.处于不同位置的Si原子呈不同大小布局数,而且由于Si3X2的对称性,2个X负电性相同.     

Vibrational study of A3In2B″O9 (A = Ba,Sr; B″ = U,W) double perovskites

Raman scattering and infrared transmittance techniques were used to investigate the room‐temperature phonon spectra of the polycrystalline Ba₃In₂UO₉, Sr₃In₂UO₉, Ba₃In₂WO₉ and Sr₃In₂WO₉ double perovskites. Although X‐ray diffraction has shown that both Ba₃In₂UO₉ and Ba₃In₂WO₉ crystallize in a disordered cubic (Pm3 m − O_h¹) structure with one formula unit per unit cell (Z = 1), Raman measurements revealed that both Ba₃In₂UO₉ and Ba₃In₂WO₉ compounds should exhibit a 1:1 ordered domains with Fm3 m symmetry, embedded in the Pm3 m matrix. Observation of a ν₁‐like vibration of the InO₆ octahedron reflects the occurrence of a two‐phonon‐like behavior due to the intrinsic occupational disorder at octahedral symmetry sites. Assignment of most of the Raman and infrared phonons is also given. Copyright © 2009 John Wiley & Sons, Ltd.     

Mn(SiO2)3(M=Fe,Co,Ni;n=1-3)团簇的几何结构、光电性质及磁性

基于密度泛函理论中的广义梯度近似系统研究M_n(SiO₂)₃(M=Fe,Co,Ni;n=1-3)团簇的几何结构、光电性质和磁学性质.结果表明:Fe,Co原子相对于Ni原子更易于在(SiO₂)₃团簇上聚集;通过分析团簇的分裂途径及其产物,发现稳定性较好的氧化硅是一种很好的用于负载过渡金属"岛膜"的载体材料;M_n(SiO₂)₃团簇的能隙恰好位于近红外光谱范围内.通过磁性分析发现,该复合团簇的磁矩主要局域在过渡金属原子周围,而且,Fe₂(SiO₂)₃和Co₃(SiO₂)₃具有相对较大的磁矩,这主要源于过渡金属原子的d轨道间相互耦合.能隙和磁性两方面性质进一步肯定了二氧化硅磁性复合材料在医学界被用作光动力靶向治疗的可观前景.     

MO-Y2O3-B2O3:Re(M=Mg,Sr;Re=Eu,Tb)的真空紫外光谱特性

采用高温固相反应法合成了掺杂Eu3 及Tb3 的17MO-7.88Y2O3-75B2O3样品,研究了它们的光谱特性,结果表明,MO-T2O3-B2O3基质在真空紫外(VUV)区有很强的吸收,MgO-Y2O3-B2O3:Eu在147nm真空紫外光激发下产生对应于Eu3 的5D0→7FJ(J=1,2,3,4)跃迁的590和613 nm强发射峰;MgO-Y2O3-B2O3:Eu中Sr的引入使材料体系在147 nm附近的吸收和在613 nm附近的发射获得明显增强;MgO-Y2O3-B2O3:Tb的真空紫外激发谱除在147 nm附近的基质吸收外,还有对应于Tb3 的4f75d→4f8跃迁位于170,178,195,204,225 nm左右的一组谱峰,两者相互叠加使得材料在真空紫外区(120～220 nm)内都有很好的吸收.     

Effects of reagent's rotational and vibrational excitations on reaction O(3P) + H2 H2(ν = 0, 3, j = 0, 3; 5; 7; 9; 12; 15) → OH + H

To investigate the effect of reagent's rotational and vibrational excitations on the stereo-dynamics of reaction product, the title reaction is theoretically simulated using the quasi-classical trajectory (QCT) method on the ³A" and ³A′ potential energy surfaces (PESs). The reaction cross section is considered as the only scalar property in this work at four different collision energies. Furthermore the vector properties including two polarization-dependent differential cross sections (PDDCSs), the angular distributions of product' rotational momentum are discussed at one fixed collision energy. Effects of reagents' rotational excitation on the reaction do exist regularly.     

MC-simulation of the 3D,q=3 Potts model

We consider theq=3 Potts model in three dimensions by Monte Carlo simulations. The microcanonical density of states is calculated as a function of the internal energy of the system. We extrapolate the data for the simulated finite systems to the thermo-dynamic limit and find a discontinuous phase transition. This method is checked in the two-dimensional case, where exact results are known.     

Stability,electronic structure,and optical properties of lead-free perovskite monolayer Cs3B2X9(B=Sb,Bi;X=Cl,Br,I)and bilayer vertical heterostructure Cs3B2X9/Cs3B’2X9(B,B’=Sb,Bi;X=Cl,Br,I)

The lead-free perovskites Cs₃B₂X₉(B=Sb,Bi;X=Cl,Br,I)as the popular photoelectric materials have excellent optical properties with lower toxicity.In this study,we systematically investigate the stable monolayer Cs₃B₂X₉and bilayer vertical heterostructure Cs₃B₂X₉/Cs3B02X9(B,B0=Sb,Bi;X=Cl,Br,I)via first-principles simulations.By exploring the electrical structures and band edge positions,we find the band gap reduction and the band type transition in the heterostructure Cs₃B₂X₉/Cs3B02X9 due to the charge transfer between layers.Furthermore,the results of optical properties reveal light absorption from the visible light to UV region,especially monolayer Cs3Sb2I9 and heterostructure Cs3Sb2I9/Cs3Bi2I9,which have absorption peaks in the visible light region,leading to the possibility of photocatalytic water splitting.These results provide insights for more two-dimensional semiconductors applied in the optoelectronic and photocatalytic fields.     

The structural properties of RbMnX<Subscript>3</Subscript> (X = F,Cl, Br) halides

The results of nonempirical calculation of energies of three polytypes (cubic, two-layer hexagonal, and six-layer hexagonal) are given for RbMnX₃ (X = F, Cl, Br) crystals. The calculation is performed using an ionic crystal model with regard for the deformability and the dipole and quadrupole polarizabilities of ions. The behavior of these crystals under the action of hydrostatic pressure is studied. It is demonstrated that, at normal pressure, the RbMnCl₃ and RbMnBr₃ crystals have a six-layer hexagonal structure. At pressures above 11 kbar, RbMnCl₃ passes to a phase with a cubic structure; RbMnBr₃ at pressures above 90 kbar passes to a phase with a two-layer hexagonal structure. The RbMnF₃ crystal under normal conditions has a cubic structure and experiences no phase transformations under the effect of pressure. The obtained results are in satisfactory agreement with the known experimental data.     

On the existence of <Emphasis Type="Bold">1, 3</Emphasis>P <Emphasis Type="Bold">o</Emphasis> resonances in H<Superscript>-</Superscript> between n = 2 and 3 H thresholds

We examine the influence of relativistic and QED effects on the existence of the ^1,3P ^o H^- resonances between n = 2 and 3 hydrogen thresholds, the relativistic and QED corrections and the coupling effects between the high singlet and triplet states are considered as first-order perturbations. We firstly obtain accurate non-relativistic resonant energies and widths of fifteen ¹P ^o resonances, and fifteen ³P ^o resonances. The fifteen ¹P ^o resonances are classified to be ₃ (2, 0) ^- _n ( 4 ? n ? 12) and ₃ (1, 1) ⁺ _n ( 3 ? n ? 8). The fifteen ³P ^o resonances are classified to be ₃ (2, 0) ⁺ _n ( 3 ? n ? 12) and ₃ (1, 1) ^- _n ( 4 ? n ? 8). We found there exist six Feshbach resonances for ₃ (2, 0) ^- _n (¹P ^o ) series, four Feshbach resonances for ₃ (1, 1) ⁺ _n (¹P ^o ) series, seven Feshbach resonances for ₃ (2, 0) ⁺ _n (³P ^o ) series, and three Feshbach resonances for ₃ (1, 1) ^- _n (¹P ^o ) series. Received 22 February 2002 Published online 24 September 2002     

Dynamics of the Weyl scale invariant non-BPS <Emphasis Type="Italic">p</Emphasis> = 3 brane

In this paper a Weyl scale-invariant p = 3-brane scenario is introduced, with the brane embedded in a higher-dimensional bulk space with N = 1, 5D Super-Weyl symmetry. Its action, which describes its long wave oscillation modes into the ambient superspace and breaks the target symmetry down to the lower dimensional Weyl W(1, 3) symmetry, is constructed by the approach of coset method.     

Mechanical Properties of Formamidinium Halide Perovskites FABX_3(FA=CH(NH_2)_2; B=Pb,Sn; X=Br,I) by First-Principles Calculations

The mechanical properties of formamidinium halide perovskites FABX_3(FA=CH(NH_2)_2; B=Pb, Sn; X=Br, I)are systematically investigated using first-principles calculations. Our results reveal that FABX_3 perovskites possess excellent mechanical flexibility, ductility and strong anisotropy. We shows that the planar organic cation FA+ has an important effect on the mechanical properties of FABX3 perovskites. In addition, our results indicate that (i) the moduli(bulk modulus B, Young's modulus E, and shear modulus G) of FABBr_3 are larger than those of FABI_3 for the same B atom, and (ii) the moduli of FAPbX_3 are larger than those of FASnX_3 for the same halide atom. The reason for the two trends is demonstrated by carefully analyzing the bond strength between B and X atoms based on the projected crystal orbital Hamilton population method.     

Physical properties of the doped manganites Ln0.5M0.5Mno3 (Ln = Pr,La; M = Sr,Ca, Ba)

We present the structural, magnetic and electrical properties of some manganese oxides such as Ln_0.5M_0.5MnO₃ (Ln = La, Pr and M = Ca, Sr, Ba) in which the average ionic radius <r_A> of the A site cation is varied while keeping the Mn³⁺/Mn⁴⁺ ratio fixed to 1. All the studied samples have a perovskite structure with rhombohedral or orthorhombic distortion. This distortion was related to the A cation size. The lattice volume increases lineraly with ( r _A) in all the range 1.179–1.3264 Å. The magnetic investigation shows that the magnetic transition temperature T _t, and magnetisation saturation M _s have similar behaviour by increasing and decreasing with (r _A). The electrical measurements show conduction by small polarons attributed to a large canting angle 9 in all the range 4–300 K in the two ferromagnetic compounds La_0.5Sr_0.5MnO₃ and La_0.5Sr_0.5MnO₃.     

Mössbauer spectroscopic studies of MIIMIVS3 (MII=Sn,Pb; MIV=Sn,Ge, Hf) and PbSnS2Se

Temperature-dependent Mössbauer experiments have been carried out to examine the lattice dynamical properties of tin sites in Sn₂S₃ and its related compounds. The differences in the lattice parameters, estimated from the temperature dependence of the area intensities for the compounds, are attributed to the characteristics of their crystal structures.     

Electrical properties of solid electrolytes with the general formula ABCD3 (A = Ag, Cu; B = Pb, Sn; C = As, Sb; and D = S, Se)

The electrical properties of AgPbSbS₃, AgSnAsS₃, AgPbSbSe₃, AgPbAsSe₃, AgSnSbSe₃, CuSnSbS₃, CuSnSbSe₃, CuSnAsSe₃, AgSnSbS₃, and AgPbAsS₃ chalcogenides are studied by the method of impedance spectroscopy with the aim of searching for materials with improved properties (increased contribution of ionic transport, decreased temperatures of onset of ionic transport, increased conductivity, the presence of ferroelectric and magnetic properties, etc.). New ionic conductors and ferroelectric semiconductors are discovered. Original Russian Text ? O.L. Kheifets, L.Ya. Kobelev, N.V. Melnikova, L.L. Nugaeva, 2007, published in Zhurnal Tekhnicheskoĭ Fiziki, 2007, Vol. 77, No. 1, pp. 90–96.     

Physical properties of ternary thallium chalcogenes Tl_2MQ_3(M = Zr,Hf; Q = S,Se, Te) via ab-initio calculations

We have reported a first principles study of structural, mechanical, electronic, and thermoelectric properties of the monoclinic ternary thallium chalcogenes Tl_2MQ_3(M = Zr, Hf; Q = S, Se, Te). The electronic band structure calculations confirm that all compounds exhibit semiconductor character. Especially, Tl_2ZrTe_3 and Tl_2HfTe_3 can be good candidates for thermoelectric materials, having narrow band gaps of 0.169 eV and 0.21 eV, respectively. All of the compounds are soft and brittle according to the second-order elastic constant calculations. Low Debye temperatures also support the softness. We have obtained the transport properties of the compounds by using rigid band and constant relaxation time approximations in the context of Boltzmann transport theory. The results show that the compounds could be considered for room temperature thermoelectric applications(ZT ～ 0.9).     

Near threshold photoionization of excited alkali atoms Ak(np) (Ak = Na, K, Rb, Cs; n = 3-6)

The effect of the polarization of the atomic core by the outer electron on near threshold photoionization of excited alkali atoms Ak(np) (Ak = Na-Cs; n=3-6) is investigated. Partial and total cross-sections for photo-ionization of the np-electron were computed utilizing the configuration interaction technique with Pauli-Fock atomic orbitals (CIPF) and including the long range core polarization potential (CP). To calculate the core polarization potential the variational principle is applied. Comparison with previous theoretical results and with available experimental data is made for the total cross-section , for the electron angular distribution parameter , for the ratio of the reduced electric dipole matrix elements and for the phase shift difference , associated with the d-wave and s-wave continua, respectively. In the comparison, new experimental results for , , and , measured for laser-excited, polarized ³⁹K(4p _3/2) atoms, have been included. Received 21 July 1999 and Received in final form 14 October 1999     

Investigation of hyperfine interactions in RMO 3 (R = La, Nd; M = Cr, Fe) antiferromagnetic perovskite oxides using PAC spectroscopy

Because of its sensitivity to point defects atomically close to probe nuclei, it is reasonable to expect that perturbed angular correlation (PAC) spectroscopy has the potential to assist in the identification of diffusion mechanisms. It is of interest to characterize under what conditions diffusing defects are visible and how the defects affect relaxation in PAC spectra. This was investigated using a stochastic model to simulate PAC spectra for the special case of non-impurity PAC probes diffusing via a simple vacancy mechanism on the Cu-sublattice in Cu₃Au-structured compounds.