Synthesis,Crystal Structure and Quantum Chemistry of Dibutyltin 3,4-Dimethoxybenzotate Compound

The dibutyltin 3,4-dimethoxybenzotate compound {[（3,4-（CH3O）2C6H3COO） Sn（Bu-n）2]2O}2 has been synthesized by the reaction of dibutyltin oxide with 3,4-dimethoxybenzoic acid. Its structure was determined by X-ray single-crystal diffraction. The crystal belongs to the triclinic system,space group P1 with a = 1.2003（2）,b = 1.2821（3）,c = 1.3666（3） nm,α = 80.50（3）,β = 65.56（3）,γ = 73.36（3）°,Z = 2,V = 1.8318（6） nm3,Dc = 1.530 Mg·m-3,μ（MoKa） = 1.413 mm-1,F（000） = 860,R = 0.0554 and wR = 0.1092. In the complex,each tin atom adopts a distorted tigonal bipyramidal structure,and the dimer structure is shaped by one Sn2O2 planar four-membered ring. The stabilities of the title complex,along with its orbital energies and composition characteristics of some frontier molecular orbitals have been investigated by means of quantum chemistry calculation methods.

Synthesis,Crystal Structure and Quantum Chemistry of a Hydration Dibenzyltin Dichloride

A novel organotin hydration dibenzyltin dichloride has been synthesized and its crystal structure was determined by X-ray diffraction. The crystal belongs to monoclinic, space group Pc with a = 1.1918（5）, b = 0.6199（2）, c = 1.1074（5）nm, β = 106.899（7）°, V= 0.7828（8）nm3, Z = 2, Dc = 1.654 g/cm3,μ（MoKa） = 19.59 cm^-1, F（000） = 384, R = 0.0564 and RwR = 0.1427. The Sn-C bonds are 0.2140（9） and 0.2152（5） nm, Sn-Cl are 0.2385（4） and 0.2497（3） nm, and Sn-O is 0.2388（7） nm. The tin atom is five-coordinated in a distorted trigonal bipyramidal configuration. The study on the title complex has been performed with quantum chemistry calculation by means of G98W package on the Lanl2dz basis set. The stability of the complex as well as the orbital energies and composition characteristics of some frontier molecular orbitals has been investigated.

ab initio CALCULATION FOR THE ELECTRONIC STRUCTURE OF GaAs/Al_xGa_(1-x) As SUPERLATTICES: CONJUGATE GRADIENT APPROACH

The electronic structure of GaAs/Al xGa 1-x As superlattices has been investigated by an ab initio calculation method—the conjugate gradient (CG) approach.In order to determine that,a conventional CG scheme is modified for our superlattices:First,apart from the former scheme,for the fixed electron density n(z),the eigenvalues and eigenfunctions are calculated,and then by using those,reconstruct the new n(z).Also,for every k z,we apply the CG schemes independently.The calculated energy difference between two minibands,and Fermi energy are in good agreement with the experimental data.

Ab Initio Calculations of the Electronic Structures of Copper Pyrites CuS2, CuSe2 and CuTe2

The electronic structures of CuS2, CuSe2 and CuTe2 with pyrite structures, within the framework the density-functional theory have been investigated. The calculated results explained the recent experimental results which show that there is no clear indication of strong electron correlations in the electronic properties of Cu pyrites, due to the dominant chalcogen p character rather than d characteristic of Cu at the Fermi level.

ab initio CALCULATION FOR THE ELECTRONIC STRUCTURE OF GaAs/AlxGa1-x As SUPERLATTICES: CONJUGATE GRADIENT APPROACH

The electronic structure of GaAs/Al xGa 1-x As superlattices has been investigated by an ab initio calculation method—the conjugate gradient (CG) approach.In order to determine that,a conventional CG scheme is modified for our superlattices:First,apart from the former scheme,for the fixed electron density n(z),the eigenvalues and eigenfunctions are calculated,and then by using those,reconstruct the new n(z).Also,for every k z,we apply the CG schemes independently.The calculated energy difference between two minibands,and Fermi energy are in good agreement with the experimental data.

Elucidating elusive quaternary selenide EuCeCuSe3:Synthesis,crystal structure,properties and theoretical studies

We report on the novel heterometallic quaternary selenide EuCeCuSe3,the fabrication of which has been a challenge until this work.The structure of the reported selenide was elucidated from the powder X-ray diffraction data,which revealed the formation of EuCeCuSe3with excellent yield(96.7%)accompanied with a minor fraction of CeSe2(3.3%),and was best solved in orthorhombic space group Pnma with the BaLaCuS3structural type.Thus,the crystal structure of the title compound completes the row of the heterometallic quaternary selenides EuRECuSe3(RE=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,Y),of which the cerium-based derivative exclusively belongs to the BaLaCuS3structural type.The distortion of the CuSe4polyhedron was compared for the whole series of EuRECuSe3compounds using theτ4-descriptor for four coordinated ions,which revealed the highest degree of distortion for the Ce3+-containing selenide,followed by the La3+-based derivative.Furthermore,the crystallographic and geometrical parameters of the reported selenide were discussed in comparison to the Ce3+-based sulfides SrCeCuS3and EuCeCuS3.Ab initio calculations of the crystal structure,a phonon spectrum and elastic constants for the crystal of EuCeCuSe3were also performed.The types and wavenumbers of fundame ntal modes were determined and the involvement of ions participating in the phonon modes was assessed.The experimental IR spectrum of the reported selenide was interpreted and found to be in agreement with the calculated spectrum.The experimental direct band gap of EuCeCuSe3was measured to be 1.36 eV that is consistent with the concept of its origin due to interband transitions between orbitals emerging mainly from 4f(valence band)and 5d(conduction band)levels of the Eu2+cation.The dependence of the Young’s modulus on the direction demonstrates the anisotropy of the elastic properties,while the Vickers hardness for EuCeCuSe3was calculated to be 5.2 GPa.Finally,the title compound is paramagnetic above 4 K.

Ab Initio Theoretical Investigation on the Geometrical and Electronic Structures of AlAu_n^(-/0)(n=2-4) Clusters

A systematic density functional theory and wave function theory investigation on the geometrical and electronic properties of A1Aun0/＂ （n = 2-4） clusters has been performed in this work. A1Aun- anions prove to possess ground states of the V-shaped C2v A1Au2, umbrella-shaped C3v A1Au3, and perfect tetrahedral Td A1Au4＂, while their neutrals favor the V-shaped CEv A1Au2, perfect planar triangular D3h A1Au3, and severely distorted Cs A1Au4, respectively. Aluminum aurides appear to be analogous to the corresponding aluminum hydrides, expect C~ A1Au4. Molecular orbitals （MOs） analyses also support this conclusion. Detailed orbital analyses indicate that Au 6s makes 94-96% and Au 5d makes 6-4% contribution to the Au-based orbitals in A1-Au bonds, which is smaller than the BAun0/- series, partially reflecting the relativistic effect of gold. The one-electron detachment energies of the anions and characteristic stretching vibrational frequencies of A1-Au bonds between 100-400 cm-1 have been calculated to facilitate future experimental characterization of these clusters.

Electronic and Optical Properties of Rare Earth Oxides: <i>Ab Initio</i>Calculation

In this work, we have investigated the electronic and optical properties of the technologically important rare earth oxide compounds—X2O3 (X: Gd, Tb) using the density functional theory within the GGA. The band structure of X2O3 have been calculated along high symmetry directions in the first brillouin zone. The real and imaginary parts of dilectric functions and the other optical responses such as energy-loss function, the effective number of valence electrons and the effective optical dielectric constants of the rare earth sesquioxides (Gd2O3 and Tb2O3) were calculated.

One-colour resonant two-photon ionization spectrum of the 1-fluoronaphthalene dimer and ab initio calculation

The one-colour resonant two-photon ionization （R2PI） spectrum of the 1-fluoronaphthalene （1FN） dimer has been studied in the wavelength range of 304 to 322 nm by using a supersonic molecular beam and time-of-flight mass spectrometry. Compared with the original band 00^0 （at 313.8 nm） of the S1 ← So transition of the 1FN monomer, a red-shifted band was observed in the 1FN dimer spectrum at about 315 nm with a relatively large linewidth, nearly 2 nm. Based on the consideration of inductive effect and ab initio calculations, this red-shifted band is assigned to the first electronic excited transition of the 1FN dimer. A possible geometric structure of the 1FN dimer is also obtained with calculations that the two 1FN molecules are combined through two hydrogen bonds which are formed between the hydrogen atom of a molecule and the fluorine atom of a neighbouring molecule. A time-dependent calculation was also carried out and the results are consistent with the experimental data.

Frist-principles Band Structures Calculation of Tin-phthalocyanine

We adopt the density function theory with generalized approximation by the Beeke exchange plus Lee-Yang-Parr correlation functional to calculate the electronic first-principles band structure of tin-phthalocyanine （SnPc）. The intermolecular interaction related to transport behavior was analyzed from the F-point wave function as well as from the bandwidths and band gaps. From the calculated bandwidths of the frontier bands as well as the effective masses of the electron and hole, it can be concluded that the mobility of the electron is about two times larger than that of the hole. Furthermore, when several bands near the Fermi surface are taken into account, we find that the interband gaps within the unoccupied bands are generally smaller than those of the occupied bands, indicating that the electron can hop from one band to another which is much easier than the hole. This may happen through electron-phonon coupling for instance, thus effectively yielding an even larger mobility for the electron than for the hole. These facts indicate that in SnPc the electrons are the dominant carriers in transport, in contrast to most organic materials.

<i>Ab-Initio</i>Calculations of 27 Electronic States of the BP⁺Ion-Molecule

The theoretical investigation of the potential energy curves, in the representation 2s+1Λ(+/-), of the 27 low-lying Doublet and Quartet electronic states of the BP+ molecular ion has been performed with the methods in quantum chemistry, the Complete Active Space Self Consistent Field (CASSCF) and the Multireference Configuration Interaction (MRCI) calculations. The harmonic vibrational frequency ωe, the inter-nuclear distance at equilibrium Re, the rotational constant Be, the electronic energy with respect to the minimum ground state energy Te, and the permanent dipole moment have also been calculated. Twenty-three new electronic states have been investigated here for the first time. The comparison between the values of the present work and those available in the literature for several electronic states shows a good agreement. These investigated data can be a conducive to further work on BP+ molecular ion in both experimental and theoretical research.

Ab Initio Calculation of the Electronic States of ScTe Molecule below 19,500 cm-1

The potential energy curves (PECs) of the16 lowest electronic states in the representation 2s+1Λ (+/-) of the molecule ScTe have been investigated via ab initio CASSCF and MRCI (single and double excitations with Davidson correction) calculations. The permanent dipole moment curves (PDMCs) and the spectroscopic constants such as vibrational harmonic frequency ωe, the internuclear distance at equilibrium Re, the rotational constant Be, and the electronic transition energy Te with respect to the ground state have been calculated for the different bound investigated electronic states. The comparison of the present results with the rare available theoretical data in literature shows an overall good agreement. To the best of our knowledge, 15 electronic states of the ScTe molecule are not yet investigated either experimentally or theoretically, they are investigated in the present work for the first time.

First-principles calculations of structural, electronic, elastic and thermal properties of phase M_2SiC(M=Ti,V,Cr,Zr,Nb,Mo,Hf,Ta and W)

The structural,electronic and elastic properties of the M_2SiC phases were studied,where M are 3d,4d,and 5d early transition metals.The valence electron concentration(VEC) effect of Ti,V,Cr,Zr,Nb,Mo,Hf,Ta and W on these properties was examined.The C_(44) saturates for a VEC value in surrounding of 8.5 for each serie.Hf-s,Ta-s and W-s electrons mainly contribute to the density of states at the Fermi level,and should be involved in the conduction properties.The distortion increases with increasing VEC and decreasing k_c/k_a factor except for the series M=Ti,V and Cr,where it is lower at the VEC value of 8.5(it follows a parabolic variation).The M_2SiC was characterized by a profound anisotropy for the shear planes(1010) and compressibility in the direction is higher than that along the cone except for W_2SiC,where it is lower.

Elastic properties and electronic structures of lanthanide hexaborides

The structural, elastic, and electronic properties of a series of lanthanide hexaborides（Ln B6） have been investigated by performing ab initio calculations based on the density functional theory using the Vienna ab initio simulation package.The calculated lattice and elastic constants of Ln B6 are in good agreement with the available experimental data and other theoretical results. The polycrystalline Young＇s modulus, shear modulus, the ratio of bulk to shear modulus B/G, Poisson＇s ratios, Zener anisotropy factors, as well as the Debye temperature are calculated, and all of the properties display some regularity with increasing atomic number of lanthanide atoms, whereas anomalies are observed for Eu B6 and Yb B6. In addition, detailed electronic structure calculations are carried out to shed light on the peculiar elastic properties of Ln B6.The total density of states demonstrates the existence of a pseudogap and indicates lower structure stability of Eu B6 and Yb B6 compared with others.

Synthesis, Crystal and Molecular Structure and Biological Activity of Dimethyl Trans-3-(2-bromophenyl)-2-methylisoxazolidine-4,5-dicarboxylate

The compound of dimethyl trans-3-（2-bromophenyl）-2-methylisoxazolidine-4,5-dicarboxylate has been synthesized and characterized by IR, 1H-NMR, 13C-NMR, 2D-NMR （COSY, NOESY, HMQC, HMBC） and UV-vis. spectroscopy techniques and single-crystal X-ray diffraction （XRD）. The biological activities of the title compound have been investigated in detail. The new compound crystallizes in monoclinic, space group C2/c with a = 26.9263（10）, b = 7.0970（2）, c = 19.8554（7） ？, and β = 126.630（2）. In addition to the single crystal structure, the molecular geometry, vibrational frequencies, chemical shifts, molecular electrostatic potential and frontier molecular orbital analysis of the title compound in the ground state have been calculated by Density Functional Theory （DFT） method.

The stabilities, electronic structures and elastic properties of Rb-As systems

The structural, electronic and elastic properties of Rb As systems （RbAs in NaP, LiAs and AuCu structures, RbAs2 in the MgCu2 structure, Rb3As in NaaAs, Cu3P and Li3Bi structures, and Rb5As4 in the A5B4 structure） are investigated with the generalized gradient approximation in tile frame of density functional theory. The lattice parameters, cohesive energies, formation energies, bulk moduli and the first derivatives of the bulk moduli （to fit Murnaghan＇s equation of state） of the considered structures are calculated and reasonable agreement is obtained. In addition, the phase transition pressures are also predicted. The electronic band structures, the partial densities of states corresponding to the band structures and the charge density distributions are presented and analysed. The second-order elastic constants based on the stress-strain method and other related quantities such as Young＇s modulus, the shear modulus, Poisson＇s ratio, sound velocities, the Debye temperature and shear anisotropy factors are also estimated.

HC_nS^+和HSC_n^+(n=1～9)结构的 ab initio 研究

应用量子化学从头计算方法，在ＨＦ／６－３１Ｇ＊水平上，采用Ｂｅｒｎｙ优化法，优化了ＨＣｎＳ＋和ＨＳＣ＋ｎ（ｎ＝１～９）两种同分异构簇离子的几何构型，计算了它们的电子总能量、相邻簇离子的能量差及其平均原子结合能。计算结果表明，ＨＣｎＳ＋比相应的ＨＳＣ＋ｎ稳定。计算结果还显示，无论是优化后的几何构型，还是各种能量值，均显示出明显的奇偶交替变化的趋势，ｎ为奇数的簇离子比相应的ｎ为偶数的簇离子稳定，这和以前得到的实验结果完全相符。此外，还计算了ＨＣｎＳ＋分别碎裂Ｈ、ＨＣ、ＨＣ２、Ｓ、ＣＳ与Ｃ２Ｓ六条解离途径的解离能。计算结果同样证明成簇碳原子数为奇数的簇离子比较稳定。

Ab initio Study on Spectral Properties of Charge-Compensated Ce^3＋ in NaF

We report an ab initio〉/I〉 study of spectral properties of Ce^3＋ doped at Na＋ site of the NaF crys-tal, with the charge imbalance compensated by two oxygen substitutions for fluoride （OF＇） in the first coordination shell or two sodium vacancies （VNa＇） in the second coordination sphere. Density functional theory calculations within the supercell model are first performed to op-timize the local structures of the charge-compensated Ce^3＋, based on which Ce-centered embedded clusters are constructed and wave function-based CASSCF/CASPT2/RASSI-SO calculations are carried out to obtain the energies of 4f1 and 5d1 levels. By comparing the calculated 4f→5d transition energies with experimental excitation spectra at low temper-atures, the lowest 4f→5d transition band peaked at 390 nm is assigned to the Ce^3＋ with charge compensation by two coordinating OF＇ substitutions, rather than to the Ce^3＋ with compensation by two VNa0 vacancies, as proposed earlier. The electronic reason for the large redshift （by -8000 cm-1） of the lowest 4f→5d transition as induced by the two nearby OF＇ substitutions is analyzed in terms of the changes in the centroid shift and crystal-field splitting.

Stacking fault energy and electronic structure of molybdenum under solid solution softening/hardening

Ab initio calculations are used to understand the fundamental mechanism of the solid solution softening/hardening of the Mo-binary system.The results reveal that the Mo-Ti,Mo-Ta,Mo-Nb,and Mo-W interactions are primarily attractive with negative heats of formation,while the interactions of Mo-Re,and Mo-Zr would be mainly repulsive with positive heats of formation.It is also shown that the addition of Re and Zr would cause the solid solution softening of Mo by the decrease of the unstable stacking fault energy and the increase of ductility.On the contrary,the elements of W,Ta,Ti,and Nb could bring about the solid-solution hardening of Mo through the impediment of the slip of the dislocation and the decrease of ductility.Electronic structures indicate that the weaker/stronger chemical bonding due to the alloying elements should fundamentally induce the solid solution softening/hardening of Mo.The results are discussed and compared with available evidence in literatures,which could deepen the fundamental understanding of the solid solution softening/hardening of the binary metallic system.

亚甲二醇二硝酸酯构型和电子结构的 ab initio 研究

采用量子化学中的从头计算（ａｂｉｎｉｔｉｏ）方法，在ＨＦ／３－２１Ｇ和ＨＦ／６－３１Ｇ＊水平上分别计算研究了亚甲二醇二硝酸酯（ＭＧＤＮ）的旋转构象和电子结构，计算所得ＭＧＤＮ绕Ｃ—Ｏ键旋转的能垒较低（约６ｋＪ／ｍｏｌ），其平面构象的能量最高．能量最低的构象（亦即最稳定构型或平衡几何构型）的２个酯基均绕Ｃ—Ｏ键旋转７７．４°．不同构型的电荷分布差异较小．