Sc2O3电子结构和光学性质的第一性原理研究

本文基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,研究了Sc2O3的电子结构、态密度和光学性质. 计算结果表明：Sc2O3是一种直接带隙半导体,其能带宽度为3.79eV,价带顶部主要由O的2p和Sc的3p3d杂化而成,导带主要由Sc的3d和O的2p构成. 同时,文中也分析了Sc2O3的介电函数、折射率、光电导率和吸收谱等光学性质. 计算得到静态介电常数 ,折射率n0=1.25,在紫外区有较大的吸收系数.     

Conformational properties of poly(p-Phenylene vinylene)

We investigate the quasiparticle conformational defects (excitons, polarons and bioplarons) in the phenylene vinylene oligomers. The conformations are determined by means of the minimization of the total Hartree-Fock energy calculated at 3–21G level. The infrared vibrational transitions are calculated and the types of vibrations are assigned. The theoretical spectra are in good agreement with the experimental vibrational spectrum of poly(p-phenylene vinylene). Presented at the Czech-Israeli-German Symposium “Dynamical Processes in Condensed Molecular Systems”, Prague, Czech Republic, 26–30 May 1997. The quantum mechanical calculations were performed on the following computers: Power Challenge XL at Prague Supercomputing Centre, Charles University, IBM Power 2 at Supercomputing Centre of the Czech Technical University and Power Challenge XL at Supercomputing Centre Brno. The work is supported by Projects No. 202/94/0453 and 202/97/1016 of the Grant Agency of the Czech Republic and by Project No. 155/96 of the Grant Agency of the Charles University.     

Ab initio SCF LCAO band structure of poly(SN)

An ab initio SCF LCAO crystal orbital calculation has been performed for the one-dimensional poly(SN) chain. The band structure obtained contains two overlapping (a σ and a π) partially filled bands of a combined width of 6.9 eV.     

First-principles energy band calculation for undoped and S-doped TiO2 with anatase structure

The electronic structure of S-doped TiO₂ with an optimized anatase structure was calculated within the framework of the density functional theory (DFT). For the calculation we built four kinds of supercells; type-A and B supercells consist of 12 and 48 atoms and a centered Ti atom is substituted for an S atom, while type-C and D supercells consist of 12 and 48 atoms and a centered O atom is substituted for an S atom. The supercells (type-B and D) were employed to adjust the S-concentration in TiO₂ to an experimental value of a few %. The changes of the lattice parameters are not significant in the type-A and B supercells. The phase transition from the tetragonal to the orthorhombic occurs in the type-C and D supercells. In the small supercell (type-A), S-related states are located in the range of −1.6 to 0 eV, and the S-states are band-like. In contrast, in the large supercell (type-B), S-related states appeared at about 0.9 eV above the top of the valence band, and the S-states are atomic-like. The localization of the S-related states is remarkable in the type-B supercell. In the type-D supercell, the S-related states were merged with the top of the valence band, and as a result the band-gap energy is narrowed by 0.7 eV. Despite a low S-concentration (3%) in the type-D supercell, the S-related states are somewhat band-like.     

Emissive pattern formation by the photoreaction of poly(p-phenylene vinylene)

The vinylene unit of a p-phenylene polymer was photo-oxidized under atmospheric oxygen to provide emittive patterns. Thin films of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-p-phenylene vinylene] (MDMO-PPV) were directly photo-patterned by UV light through a photo-mask having 1 μm-wide lines. The absorption and fluorescence studies on the MDMO-PPV film by UV irradiation indicated that the photo-patterning was mainly originated from the oxidation of the vinylic bonds to give carbonyl (CO) containing polymers. The patterned MDMO-PPV film was applied to an electroluminescent cell, which showed 20 μm-wide luminescent line patterns at applied potential of 5 V.     

聚对苯撑及其烷氧基衍生物的能带研究

利用扩展Hückel分子轨道方法，运用BICON-CEDiT程序包计算了聚对苯撑及其系列烷氧基取代物的一维能带结构.计算结果表明：聚合物的能带结构在很大程度上受到杂原子、侧链等因素的影响，这与已知的实验结果相符；随着烷氧基侧链中C原子数的改变，聚合物的带隙呈现规律性变化.理论计算得到的带隙值与已有的实验观察值符合得相当好.     

Structure development in curing of poly(phenylene sulfide)

The structure development during melt curing of poly(phenylene sulfide) (PPS) is reported. The changes in the structure were monitored using various characterization techniques such as differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy, and optical microscopy. It was observed that the thermal parameters such as melting point and heat of fusion are very sensitive to the structural changes and can be effectively used to monitor the curing process. The effect of curing environment was also investigated, and it was found that the rate of change of structure is considerably higher in air than in nitrogen. The results are discussed on the basis of the different mechanisms for curing of PPS.     

First-principles energy band calculation for undoped and N-doped InTaO4 with layered wolframite-type structure

The electronic structures of undoped and N-doped InTaO₄ with optimized structures are calculated within the framework of the density functional theory. Calculated lattice constants are in excellent agreement with experimental values, within a difference of 2%. The valence band maximum (VBM) is located near the middle point on the ZD line and the conduction band minimum (CBM) near the middle point on the DX line. This means that InTaO₄ is an indirect-gap material and a minimum theoretical gap between VBM and CBM is ca. 3.7 eV. The valence band in the range from −6.0 to 0 eV mainly consists of O 2p orbitals, where In 4d5s5p and Ta 5d orbitals are slightly hybridized with O 2p orbitals. On the other hand, the conduction band below 5.5 eV is mainly composed of the Ta 5d orbitals and the contributions of In and O orbitals are small. The band gap of N-doped InTaO₄ decreases by 0.3 eV than that of undoped InTaO₄, because new gap states originating from N 2p orbitals appear near the top of the valence band. This result indicates that doping of N atoms into metal oxides is a useful method to develop photocatalysts sensitive to visible light.     

(Zn,Al)O电子结构第一性原理计算及电导率的分析

采用第一性原理平面波赝势方法和广义梯度近似计算了ZnO与(Zn,Al)O的电子结构.结合分子轨道理论,从原子布居、键布居、能带结构和态密度角度分析了掺Al前后ZnO的成键情况及对电子间相互作用的影响.利用第一性原理计算结果理论推导计算了(Zn,Al)O的载流子浓度并进一步分析了ZnO电导率的变化情况.与实验结果比较可知,掺Al后ZnO载流子浓度增加,并且ZnO的电导率比未掺杂时有了显著的提高. 关键词： 第一性原理 电子结构 电导率 (Zn Al)O     

Semi-empirical APW calculation of the band structure of silicon

We propose a modification to the usual augmented-plane-wave muffin-tin approximation approach which fits exactly the measured value of the band gap of Si. The method involves one adjustable parameter which is introduced by a uniform shift of the s-like logarithmic derivatives. The results are in good agreement with those of the empirical pseudopotential method not only for the gap but also for an energy range of approximately 3eV from the top of the valence band.