First-principle study of Mg adsorption on Si（111） surfaces

We have carried out first-principle calculations of Mg adsorption on Si(111) surfaces. Different adsorption sites and coverage effects have been considered. We found that the threefold hollow adsorption is energy-favoured in each coverage considered, while for the clean Si(111) surface of metallic feature, we found that 0.25 and 0.5 ML Mg adsorption leads to a semiconducting surface. The results for the electronic behaviour suggest a polarized covalent bonding between the Mg adatom and Si(111) surface.     

Computation of electronic structure and magnetic properties of strongly correlated materials with LDA+DMFT method

In this review, we describe general ideas of the LDA+DMFT method which merges dynamical mean-field theory (DMFT) and density functional theory (in particular the local density approximation (LDA)). Nowadays, the LDA+DMFT computational scheme is the most powerful numerical tool for studying physical properties of real materials and chemical compounds. It incorporates the advantage of DMFT to treat the full range of local dynamical Coulomb correlations and the ability of band methods to describe material-specific band dispersion caused by the lattice periodicity. We briefly discuss underlying physical ideas of LDA+DMFT and its mathematical implementation. Then different algorithms applied to solution of the DMFT impurity problem are briefly described. We then give examples of successful applications of the LDA+DMFT method to study spectral and magnetic properties of recently synthesized compounds like pnictide superconductors as well as classic charge-transfer systems NiO and MnO.     

长程电子关联对有限长聚乙炔链中极化子态的影响

本文采用扩展Hubbard模型, 加上长程关联哈密顿量,在自然边界条件下用自洽场方法研究了有限长反式聚乙炔链中极化子的问题。计算了长程电子关联对极化子的影响并计算了极化子的长程关联能。计算发现长程电子关联使极化子的位形变宽变浅(局域性减弱),在极化子区域,长程电子关联能比平均长程电子关联能要大。当链长增加到100格点以上时,电子极化子和空穴极化子的平均关联能趋于-0.1663eV,而在极化子区域,电子极化子和空穴极化子的平均关联能趋于-0.1868eV。     

Investigation of In-Gap States in SmB6

We have investigated the low temperature properties of the narrow-gap semiconductor SmB₆ by means of electrical resistivity and specific heat measurements. Results imply that the residual resistivity below about 3 K is non-activated and the corresponding state, which is formed within the in-gap states, has a metallic-like nature. Heat capacity measurements confirmed the metallic-like properties of the in-gap states and revealed, moreover, an enhancement of the specific heat below 2 K which is more expressive for the sample with a lower amount of impurities. The observed behaviour can be attributed to the formation of a coherent state within the in-gap states of this compound.     

The effects of contact configurations on the rectification of dipyrimidinylben diphenyl diblock molecular junctions

The transport properties of a conjugated dipyrimidinyl-diphenyl diblock oligomer sandwiched between two gold electrodes, as recently reported by [Díez-Pérez et al. Nature Chem. 1 635 (2009)], are theoretically investigated using the fully self-consistent nonequilibrium Green's function method combined with density functional theory. Two kinds of symmetrical anchoring geometries are considered. Calculated current-voltage curves show that the contact structure has a strong effect on the rectification behaviour of the molecular diode. For the equilateral triangle configuration, pronounced rectification behaviour comparable to the experimental measurement is revealed, and the theoretical analysis indicates that the observed rectification characteristic results from the asymmetric shift of the perturbed molecular energy levels under bias voltage. While for the tetrahedron configuration, both rectification and negative differential conductivity behaviours are observed. The calculated results further prove the close dependence of the transporting characteristics of molecular junctions on contact configuration.     

溶液酸碱性对低聚苯亚乙炔基分子结电输运性质的影响

结合密度泛函理论和非平衡格林函数方法计算了溶液酸碱性对低聚苯亚乙炔基分子结电输运性质的影响,此低聚苯亚乙炔基分子中两个不同位置的H原子被氨基和羧基取代.通过质子化和去质子化模拟酸性溶液和碱性溶液对分子结构的影响.计算结果表明:中性环境下分子器件具有良好的导电性和微弱的整流效应;碱性溶液中羧基去质子化后,分子器件电流值增长近一倍,但整流效应变化不明显;酸性溶液中氨基质子化后,分子器件正向偏压导电性能略微降低,但整流方向发生明显反转,且与中性环境下的情况相比,整流比提高了近三倍.提出了一种利用化学手段控制分子结导电能力和整流性能的方法.     

Electronic structure of Mg–Zn-based compounds

We present a comparison between calculated densities of states of the Laves phase MgZn₂ and hexagonal Mg₂₈Zn₆₅Y₇ and experimental results obtained using both X-ray emission and photoabsorption spectroscopy techniques. We show that there is general agreement between both sets of data for both alloys. We also point out that the two samples retain a metallic character, yet the hexagonal approximant of the Mg–Zn–Y quasicrystal family is less metallic than the Laves phase.     

DNA分子链电子结构特性研究

在单电子紧束缚近似下，建立了一维无序二元DNA分子链模型，计算了链长为2×10⁴个碱基对的DNA分子链的电子态密度、局域化特性，并探讨了碱基对的不同组分、格点能量无序度对电子局域态的影响.结果表明：由于DNA分子链中格点能量无序及碱基对的不同组分的存在，其电子波函数呈现出局域化的特性，而局域长度作为衡量电子局域化程度的一个尺度，受碱基对的组分及格点能量无序度的影响. 关键词： DNA分子链 电子结构 电子局域态 局域长度     

单壁碳纳米管电子输运特性的稳定性分析

基于变形单壁碳纳米管能量色散关系,计算了碳纳米管最低导带的电子速度及有效质量随形变系数变化的各种曲线,以此推测碳纳米管输运性质的稳定性问题.计算结果表明：对于特定类型的碳纳米管,只当其形变发生在某特定方向、且处于低形变（形变系数ε≤002 ）区时,电子平均速度v_mean及平均有效质量m^*_mean随形变改变才会很小（相对改变量≤2%）,这意味着此时的碳纳米管低偏压电子输运性能是基本稳定的.而其他形变情形,电子平均速度v_mean或电子平均有效质量m^*_mean或两者随形变变化明显,甚至有跃变,这意味着其低偏压电子输运性能是不稳定的,甚至极不稳定. 关键词： 变形单壁碳纳米管 电子速度 电子有效质量 输运性能稳定性     

Structural properties of thermal evaporated SnTe thin films

Summary The morphological structure of SnTe very thin films is here studied by X-ray photoemission spectroscopy, by transmission electron spectroscopy and by X-ray diffraction. The analisys of experimental data evidences the superficial confinement of Sn, with different oxidation states, and the Te excess in the inner layers. The energy shift of the valence band peaks is attributed to modifications induced by the nonstoichiometry of the compound. Preliminary Hall and resistivity measurements seem to confirm the structural obtained results.     

Excitation of the Li isoelectronic sequence

Summary The inner-shell excitation 1s ²2s ² S ^e→1s2s ²² S ^e, which leads to autoionization (Auger transition), as well as the outer-shell excitation 1s ²2s ² S ^e→ 1s ²2p ² P ⁰ transitions have been investigated in Li, Be⁺, B²⁺ and C³⁺ ions of the lithium isoelectronic sequence employing the configuration interaction wave functions for both the initial and final states involved in the transition matrix element. Results are compared with other available theoretical predictions and experimental observations. Comparison shows that our present theoretical results are encouraging. A part of this work was done while the author was Research Director and Professor, CNRS Laboratory, University of Paris-Sud, Paris and Observatoire de Paris, Meudon, Paris, France.     

Electronics with and on paper

Today there is a strong interest in the scientific and industrial community concerning the use of biopolymers for electronic applications, driven mainly by low‐cost and disposable applications. Adding to this interest, we must recognise the importance of the dream of wireless auto‐sustained and low‐energy‐consumption electronics. This dream can be fulfilled by cellulose paper, the lightest and the cheapest known substrate material, as well as the Earth's major biopolymer and of tremendous global economic importance. Most of the paper used up to now is optimised in terms of the required mechanical and physical properties to be used as the support of inks of different origins. In the future, specific electronic heterogeneous paper sheets should be fabricated aiming to get paper fibers with required bulk and surface functionalities, proper water/vapour barrier, size and diameter/thickness of the fibrils and full paper thickness. This will be the function of components/devices to be incorporated/integrated such as thin‐film transistors, complementary metal oxide semiconductor devices, passive electronic components (resistances, inductors and capacitors), memory transistors, electrochromics and thin‐film paper batteries. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nanometer Scale Electrical Characterization of Artificial Mesostructures

In this article, we review advances in experimental techniques for the electrical characterization of artificial mesostructures from nanometer to micrometer size. As the scale of electronic devices is rapidly approaching the 100-nm benchmark, new tools are becoming necessary to study and characterize them. We are also at a point where new tools to fabricate these devices are becoming increasingly relevant. We discuss the various characterization techniques applicable to objects of this scale, with particular emphasis on scanned probe methods.     

低偏压下单层碳纳米管的输运特征

系统地计算了各种手性碳纳米管最低导带的电子速度和有效质量的变化规律,在此基础上推断手性碳纳米管低偏压下的输运特征,计算表明:在低偏压电子输运时,同一系列(手性角相同)的各种手性金属碳纳米管的输运性质相同,与管径无关,但不同系列的手性金属碳纳米管的输运性质有明显区别;而同一系列的各种手性半导体型碳纳米管的输运性质有一定差异,但不同系列的手性半导体型碳纳米管的输运性质有着显著差异.这一结果说明:碳纳米管在低偏压下的输运特征与系列有着密切的关系,手性角是决定各种碳纳米管在低偏压下具有不同输运性质的最关键的几何参 关键词： 碳纳米管 手性角 电子速度 有效质量     

Effect of the exchange potential and of the cut-off radii on the energy bands of α-quartz

Summary An analysis of the effect of different forms of the exchange potential and values of the cut-off radii in the mixed-basis calculation of the band structure of α-quartz is presented. An optimal choice is made and the corresponding bands are computed and discussed.

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Riassunto Si presenta un’analisi dell’effetto che diverse forme del potenziale di scambio e diversi valori dei raggi di cut-off hanno sulla struttura a bande del quarzo-α, calcolata col metodo della base mista. Si fa una scelta ottimale e le corrispondenti bande sono calcolate e discusse.

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Резюме Проводится анализ влияния различных форм обменного потенциала и величин радиуса обрезания на зонную структуру α-кварца. Предлагается оптимальный выбор и вычисляются соответсвующие зоны. Проводится обсуждение полученных результатов.

     

Interaction of Anionic Forms of Fe-Octaethylporphyrin With Methanol

The electron absorption spectra of protonation products of ClFe(III) anions-octaethylporphyrin (Fe(III)OEP) have been investigated. The spectra of monoanions (Fe(II)OEP) and dianions (Fe(I)OEP) in tetrahydrofuran remain practically unchanged on protonation of these reduced forms by methanol, whereas in the spectra of protonation products of tri- and tetraanions absorption bands characteristic of -monoanions and Zn-phlorins are observed. These data are interpreted as proof of the -anionic character of the ligand, i.e., the excess electron density in three- and four-electron reduced forms of FeOEP is concentrated not only on the d-orbitals of the Fe ion, but also in the cyclic system of the tetrapyrrole ligand.     

Electric-dipole oscillator strengths of 2p 63s 2 S e →2p 53s 2 2 P 0 transition in MgII,Al III and SiIV ions of the NaI isoelectronic sequence

Summary Electric-dipole oscillator strengths, of both the length and velocity forms, for the inner-shell excitation 1s ²2s ²2p ⁶3s ² S ^e →1s ²2s ²2p ⁵3s ^{2 2} P ⁰ transition, which leads to autoionization (Auger transition), in Mg II, Al III and SiIV ions of the sodium isoelectronic sequence have been calculated using the approach suggested by one of us (Tiwary) in the case of the Fe¹⁵⁺ ion. Our present calculated results demonstrate that the Tiwary approach is capable of yielding encouraging results. A part of this work was done while the author was Research Director and Professor, CNRS Laboratory, University of Paris-Sud, Paris and Obsevatoire de Paris, Meudon, Paris, France.     

The quantum mechanics of rotating and translating molecules: Semi-classical treatment. —I.

Summary The emergence by classical computer simulation of defintive evidence for statistical correlation between molecular rotation and translation leads to a new appraisal of the quantum structure of rotational absorption in the microwave and far infrared. The classical correlation implies that the accepted theory of ?pure rotational? quantum absorption is only a first approximation. The translation of a molecule in some environments affects its own quantized absorption due to rotation. The number of allowed quantum transitions is increased from the accepted theoretical ΔJ=±1 to ΔJ=±1, ±2, ±3 for all dipolar molecules. These results are obtained using group theory, which also predicts that translation rotation effects increase the number of allowed transitions for eachJ quantum number and therefore affect the intensity distribution of the absorption lines. These results modify fundamentally the accepted theory of quantized rotation. Theoretically, the well-known δJ=1 distribution is supplemented by further distributions at δJ=2 and δJ=3.

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Riassunto Il fatto che sia emessa una prova definitiva con simulazione al computer classica per la correlazione statistica tra la rotazione molecolare e la traslazione porta ad una nuova valutazione della struttura quantistica dell’absorbimento rotazionale nelle microonde e nel lontano infrarosso. La correlazione classica implica che la teoria accettata di un absorbimento quantistico ?rotazionale puro? sia solo una prima approssimazione. La traslazione di una molecola in alcuni ambienti influenza il proprio absorbimento quantizzato a causa della rotazione. Il numero di transizioni quantistiche permesse è aumentato dal valore teorico accettato ΔJ=±1 a ΔJ=±1, ±2, ±3 per tutte le molecole dipolari. Questi risultati sono ottenuti usando la teoria di gruppo che prevede anche che gli effetti della rotazione di traslazione aumentino il numero di transizioni permesse per ciascun numero quanticoJ e che quindi influenzino la distribuzione d’intensità delle linee di absorbimento. Questi risultati modificano fondamentalmente la teoria accettata della rotazione quantizzata. Teoricamente la distribuzione ben nota a ΔJ=1 è integrata da altre distribuzioni a ΔJ=2 e ΔJ=3.

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Резюме С помощью классического компьютерного моделирования обнаружено подтверждение статистической коррельции между молекульрными вращением и трансляцией. Этот результат приводит к новой оценке квантовой структуры ротационного поглощения в микроволновой и далекой инфракрасной областях. Классическая корреляция подразумевает, что принятая теория ?чистого ротационного⩉ квантового поглощения представляет только первое приближение. Трансляция молекулы в некоторой окружающей среде изменяет квантованное поглоцение, вследствие вращения. Число разешенных квантовых переходов увеличивается от теоретической величины ΔJ=±1 до ΔJ=±1, ±2, ±3 для всех диполчных молекул. Эти результаты получены, использыя теорию групп, которая также предсказывает, что эффекты трансляции и вращения увеличивают число разрешенных переходов для каждого квантового числаJ и, следовательно, изменяют распределение интенсивности для для яиний поглощения. Полученные результаты существенно видоизменяют принятую теорию квантованного вращения. Теоретически хорошо известное ΔJ=1 распределение дополяется распределениями ΔJ=2 и ΔJ=3.

     

卷曲效应对单壁碳纳米管电子结构的影响

利用计入卷曲效应的单壁碳纳米管(SWCNT)的能量色散关系,计算最低导带的电子速度及有效质量,并与不计入卷曲效应的结果进行了比较.计算结果表明:卷曲效应对电子速度及有效质量的影响与SWCNT的类型密切相关,金属锯齿型SWCNT对卷曲效应最为敏感,其次是扶手椅型SWCNT,最不敏感的是半导体锯齿型SWCNT.由此可以推断,卷曲效应对金属锯齿型SWCNT电子结构及低偏压输运特性影响最大,其次是扶手椅型SWCNT,影响最不明显的是半导体锯齿型SWCNT.这些结果与实验测量及密度泛函理论计算结果完全一致. 关键词： 单壁碳纳米管 卷曲效应 电子速度 电子有效质量