Density Functional Theory Studies on the High-pressure Behavior of Crystalline 5,7-Dinitrobenzo-1,2,3,4-tetrazine-1,3-dioxide

The structural and electronic properties of the solid 5,7-dinitrobenzo-1,2,3,4-tetrazine-1,3-dioxide（DNBTDO） under the hydrostatic pressure of 0~100 GPa were investigated using density functional theory method. The predicted crystal structure with the LDA/CA-PZ functional agrees well with the experimental data at the ambient pressure. The structural results show that the b axis is the most compressible, whereas the a and c axes both have slight variation with pressure. The band gap generally decreases with the increasing pressure, which shows that the DNBTDO molecular crystal undergoes an electronic phase transition from semiconductor to metallic system. Through the analysis of band gap, the title compound is most sensitive at 70 GPa. The density of states analysis indicates that the strong peaks split into some small peaks and become wider under compression, which shows the increase of charge overlap and delocalization among the bonded atoms in the system.

Density Functional Theory Study of C_2H_x(x=4～6) Adsorption on the Fe(110) Surface

The density functional theory（DFT） and self-consistent periodic calculation were used to investigate the C2Hx（x = 4～6） species adsorption on the Fe（110） surface. The adsorption energy and equilibrium geometry of the species C2Hx（x = 4～6） on four possible sites（top,hcp,SB and LB） on the Fe（110） surface were predicted and compared. Mulliken charges and density of states analysis of the most stable site have been discussed. It is found that the species of C2H6 and C2H5 are adsorbed strongly on the Fe（110） surface with calculated adsorption energy of -80.24 and -178.89 kJ·mol^-1 at the Fe-LB（long-bridge） ,respectively. However,the C2H4 is adsorbed strongly on the Fe（110） surface with calculated adsorption energies of -114.96 kJ·mol^-1 at the top. The results indicate that the charge transferring process can be completed by chemisorption between Fe（110） surface and the species. Moreover,the chemical bands can be formed by chemisorptions between the Fe（110） surface and the species,too.

Transformations and Tautomeric Equilibrium among Different Intermediates in Proline-Catalyzed Reactions of Aldehydes or Ketones

The enamines, iminium ions, and oxazolidinones are thought to be the key intermediates in the proline-catalyzed reactions of aldehydes or ketones, but there is an extensive contro- versy about their roles. Here, the corresponding transition states connecting any two of the three kinds of species are located at the wB97XD/6-311＋＋G＊＊ level of theory. The calcula- tions demonstrate that the oxazolidinones are the predominant species in both the gas phase and solvents; there exists tautomeric equilibrium among these species and the equilibriums are controlled by the employed solvents and temperature in the reaction. These results demonstrate that the concentration and role of the mentioned species are controlled by the employed solvent and temperature. A new reaction pathway is presented herein for the trans- formation between iminium ions and oxazolidinones through iminium ion-water complex and oxazolidinone-water complex. The calculations demonstrate that the rate-limiting step in proline-catalyzed Mannich reaction between acetaldehyde/keteones and N-Boc imines is the formation of the C-C bond rather than the intermediates tautomerization. These calculations rationalize the available experimental observations and can be valuable in optimizing the experimental conditions of asymmetric organic-catalyzed reactions of aldehydes or ketones.

Structural, Photoluminescent and Theoretical Evidence for Ligand-unsupported Argentophilic Interactions in a Supramolecular Aggregate of [Ag_2(Hida)(NH_3)_2]

A new neutral [Ag2（Hida）（NH3）2] molecule （1, H3ida = 1H-imidazole-4,5-dicarboxylic acid） has been synthesized and structurally characterized by single-crystal diffraction. Compound 1 crystallizes in monoclinic, space group C2/c with a = 18.3928（8）, b = 8.3299（5）, c = 13.682（7） A, β = 113.179（2）°, V = 1926.9（10）A^3, Z = 8 and Dc = 2.784 g·cm^-3. In the solid state, this disilver（I） compound can aggregate to furnish the energetically stable ligand-unsupported Ag^I-Ag^I interaction concomitant with significant photoluminescence changes in different aggregate states, and such argentophilicity interaction is also supported by molecular orbital calculations.

Theoretical and Experimental Studies on the Reaction Mechanism of Cl_2 + I_2 = 2ICl

The gas phase reaction mechanism of Cl2 ＋ I2 = 2ICl has been theoretically investigated by DFF method at the B3LYP/3-21 G＊ level. Transition states of three reaction channels were consequently given. The results indicate that in the title reaction the least activation energy of bi-molecular reaction was smaller than the dissociation energies of I2 and Cl2, and thus the reaction mechanism was the course of molecule-molecule interaction at low reaction rate. If other factors such as illumination were taken into account, I2 could dissociate into I atoms and then react with Cl2, or Cl2 dissociates into CI atoms and reacts with I2. These were photochemical reactions with high reaction speed. The theoretical results were further validated with absorbance measurement at 516 nm.

西部地区经济增长质量研究

从经济增长效率、经济结构优化、经济稳定性、人民生活幸福、生态环境和谐五个维度构建一套经济增长质量评价指标体系,并据此运算用熵权法与线性加权法组合测算出2004~2017年西部地区12个省市的经济增长质量指数,随后运用变异系数法和系统聚类法分析了经济增长质量的地区差异,最后采用核密度估计方法分析西部地区经济增长质量水平的分布动态与特征,主要结论有:西部地区经济增长质量存在地区和增长率差异,后期政策应有针对性。

Structural,electronic and elastic properties of YCu from first principles

The structural, electronic and elastic properties of YCu compound in the B2 （CsCl） phase were investigated using the density functional theory （DFT） within the generalized gradient approximation （GGA）. The electronic density of states （DOS） obtained in this way accorded weU with the results of a recent study utilizing the full-potential linearized augmented plane wave （FLAPW） method. We also found that the density of d-states at the Fermi energy was low. The calculated equilibrium properties such as lattice constant, bulk modulus and its first derivative, and the elastic constants were in good agreement with experimental and theoretical results.

Theoretical Investigation on the Charge Transport Properties of 2,5-Di(cyanovinyl)-thiophene/furan with the Kinetic Monte Carlo Method

Exploring, designing, and synthesizing novel organic field-effect transistor （OFET） materials have kept an important and hot issue in organic electronics. In the current work, the charge transport properties for 2,5-di（cyanovinyl）thiophene/furan crystal associating two pentafluorophenyl units linked via the azomethine bond, CTE and CFE have been theoretically investigated by means of density functional theory （DFT） calculations coupled with the incoherent charge-hopping mechanism and the kinetic Monte Carlo simulation. Results show that these two compounds possess remarkably low-lying HOMO （-7.0 eV） and LUMO （-4.0 eV） levels, as well as large electron affinities （〉 3.0 eV）, which indicate their high stability exposed to air as promising OFET materials. However, the ph value at room temperature （T = 300 K） is predicted to be 2.058x10^7 cm26Vl·s-1, and the is as low as 9.834^10-8 cm2-V-l.s-1 for CFT crystal. Meanwhile, these two values are 7.561 x 10-8 and 8.437 x 10-8 cm2.V-I.s-1 for the CFE crystal, respectively. Furthermore, the simulation of angle-dependent mobility in the a-b, a-c, and b-c crystal planes shows that the charge transport in CTE and CFE crystals is remarkably anisotropic, which maybe is helpful for the fabrication of high-performance OFET devices.

Insight of the Structures and Properties on 2-Thioxanthine Complexes with One Hg^(2+)and Two Cl^-Ions:a Theoretical Investigation

The molecular structures of fifteen possible 2-thioxanthine（2TX） complexes with one Hg^2＋ and two Cl-ions were fully optimized using density functional theory B3PW91/6-311＋＋G^＊＊ method. The effective pseudo potential LANL2DZ basis set was used for metal Hg^2＋ion. The vibrational analysis was also carried out at the same level. The bond lengths, bond angles, zero point energies, Gibbs free energies, thermodynamic energies and relative energies of all the complexes were obtained. The NBO analysis for natural charge and the second order perturbation energy values was carried out for three stable complexes and the IR spectroscopy of the two complexes was assigned to the experimental data. The results show that the 2-thioxanthine complexes with one Hg^2＋ and two Cl^-ions were formed and the complexes resulting from the thione tautomer are more stable than that of the thiol ones. The order of three complexes with relative lower energy is 2TX（1,3,7）-Hg^2＋-2, 2 TX（1,3,7）-Hg^2＋-1 and 2 TX（1,3,9）-Hg^2＋. The calculated IR spectroscopy of the two complexes agreed with the experimental data.

A new C=C embedded porphyrin sheet with superior oxygen reduction performance

C2 is a well-known pseudo-oxygen unit with an electron affinity of 3.4 eV. We show that it can exhibit metal-ion like behavior when embedded in a porphyrin sheet and form a metal-free two-dimensional material with superior oxygen reduction performance. Here, the positively charged C=C units are highly active for oxygen reduction reaction （ORR） via dissociation pathways with a small energy barrier of 0.09 eV, much smaller than that of other non-platinum group metal （non-PGM） ORR catalysts. Using a microkinetics-based model we calculated the partial current density to be 3.0 mA/cm2 at 0.65 V vs. a standard hydrogen electrode （SHE）, which is comparable to that of the state-of-the-art Pt/C catalyst. We further confirm that the C=C embedded porphyrin sheet is dynamically and thermally stable with a quasi-direct band gap of 1.14 eV. The superior catalytic performance and geometric stability make the metal-free C=C porphyrin sheet ideal for fuel cell applications.

Prediction of large-gap quantum spin hall insulator and Rashba-Dresselhaus effect in two-dimensional g-TIA （A = N, P, As, and Sb） monolayer films

A new family of two-dimensional （2D） topological insulators （TIs） comprising g-TIA （A = N, P, As, and Sb） monolayers constructed by T1 and group-V elements is predicted by first-principles calculations and molecular-dynamics （MD） simulations. The geometric stability, band inversion, nontrivial edge states, and electric polarity are investigated to predict the large-gap quantum spin Hall insulator and Rashba-Dresselhaus effects. The MD results reveal that the g-T1A monolayers remain stable even at room temperature. The g-T1A （A = As, Sb） monolayers become TIs under the influence of strong spin-orbit couplings with large bulk bandgaps of 131 and 268 meV, respectively. A single band inversion is observed in each g-T1A （A = As, Sb） monolayer, indicating a nontrivial topological nature. Furthermore, the topological edge states are described by introducing a sufficiently wide zigzag-nanoribbon. A Dirac point in the middle of the bulk gap connects the valence- and conduction-band edges. The Fermi velocity near the Dirac point with a linear band dispersion is -0.51 × 106 m/s, which is comparable to that of many other 2D nanomaterials. More importantly, owing to the broken inversion symmetry normal to the plane of the g-T1A films, a promising Rashba-Dresselhaus effect with the parameter up to 0.85 eV-A is observed in the g-T1A （A = As, Sb） monolayers. Our findings regarding 2D topological g-T1A monolayers with room-temperature bandgaps, intriguing topological edge states, and a promising Rashba-Dresselhaus effect are of fundamental value and suggest potential applications in nanoelectronic devices.

Linear-scaling computation of excited states in time-domain

The applicability of quantum mechanical methods is severely limited by their poor scaling.To circumvent the problem,linearscaling methods for quantum mechanical calculations had been developed.The physical basis of linear-scaling methods is the locality in quantum mechanics where the properties or observables of a system are weakly influenced by factors spatially far apart.Besides the substantial efforts spent on devising linear-scaling methods for ground state,there is also a growing interest in the development of linear-scaling methods for excited states.This review gives an overview of linear-scaling approaches for excited states solved in real time-domain.

Enhanced adsorption of carbonyl molecules on graphene via π-Li-π interaction: a first-principle study

Carbonyl compounds with elements of C, H, and O and reversible redox-active centers are promising elec- trode materials in rechargeable batteries owing to their high theoretical capacity, structure flexibility and resources abun- dance. However, the low conductivity and the dissolution of active molecules in organic electrolyte limit the practical ap- plication. Immobilizing the carbonyls on graphene provides a simple approach to address these two issues. However, most reported interaction between carbon-based substrates and carbonyl compounds is weak π-π interaction, which is not strong enough to prohibit the detachment of active ma- terials from carbon surface, and thus leading to undesirable cycling performance. Herein, we applied the first principle calculations to study the carbonyls-graphene interaction and found that the weak rc-a interaction can be rationally converted to the strong a-Li-~~ interaction via introducing the groups containing Li atoms. The introduced Li atoms can cooperatively bind with the two aromatic a components through the covalent Li-carbonyl compounds interaction and Li-graphene interaction. The concept of ~（-Li-Tr interaction provides a versatile method to suppress the dissolution of active materials and increase the electronic conductivity at the same time, which gains insight into the design of organic electrode materials for rechargeable batteries with high performance.

Is There a Minimum Electrophilicity Principle in Chemical Reactions？

For 25 simple reactions, the changes of the hardness （△η）, polarizability （△α） and electrophilicity index （△ω） and their cube-roots （△η^1/3, △α^1/3, △ω^1/3） were calculated. It is shown that although the Maximum Hardness and Minimum Polarizability Principles are not valid for all reactions, but in most cases △ω^1/3〈0, whereas we always find △ω〈0. Our observation implies to this fact that for those chemical reactions in which the number of moles decreases or at least remains constant, the most stable species （reactants or products） have the lowest sum of electrophilicities. In other words ＂the natural direction of a chemical reaction is toward a state of minimum electrophilicity＂. This fact may be called Minimum Electrophilicity Principle （MEP）.

ASYMPTOTIC NORMALITY OF THE NEAREST NEIGHBOR HAZARD ESTIMATES

The nearest neighbor (n.n.) and its related methods are widely used in density and hazard function estimations. Even though the asymptotic normality of the n.n. density estimate is well known (see [1]), similar results for the n.n. hazard estimate have not been shown in the literature. In this paper, we develop a different approach to deal with the n.n. type estimator. For a mixed censorship-truneation model, we show that, under mild conditions, the n. n. estimate can be approximated by an estimate formed with a proper fixed bandwidth sequence and derive the asymptotic normality as a consequence.