Electronic Structures of LixV2O5 (x=0.5 and 1): A Theoretical Study

The electronic properties of α‐Li_xV₂O₅ (x=0.5 and 1) are investigated using first principle calculations based on density functional theory with local density approximation. Different intercalation sites for Li in the V₂O₅ lattices are considered, showing different influences on the electronic structures of Li_xV₂O₅. The lowest total energy is found when Li is only intercalated along the c axis between two bridging oxygen ions of sequential V₂O₅ layers. The intercalation of Li into V₂O₅ does not change the electron transition property of V₂O₅, which is an indirect band gap semiconductor, but leads to a reduction of vanadium ions and an increase of the Fermi level of Li_xV₂O₅ arising from the electron transfer from the Li 2 s orbital to the initially empty conduction band of the V₂O₅ host.     

甲醇在Pt-Fe(111)/C表面吸附的理论研究

采用密度泛函理论和周期平板模型相结合的方法, 对CH3OH分子在Pt-Fe(111)/C表面top, fcc, hcp和bridge位的吸附模型进行了构型优化、能量计算, 结果表明bridge位是较有利的吸附位. 掺杂后费米能级的位置发生了右移, 价带和导带均增宽, 极利于电子-空穴的迁移, 这对提高催化活性是非常有利的. 考察抗中毒性发现: CO在Pt(111)/C面上的吸附能比甲醇吸附能要高, CO在Pt-Fe(111)/C的吸附能比甲醇吸附能要低, 可说明CO在Pt(111)/C面上有中毒效应, 而Pt-Fe(111)/C的抗CO中毒能力增强, 是催化氧化甲醇良好的催化剂.     

CH3SOx (x＝0, 1)与三线态Oy (y＝1, 2, 3)反应机理的理论研究

采用B3LYP方法和6-311G(d, p)基组对CH₃S及其氧化后继物CH₃SO与O_y (y＝1, 2, 3)反应形成酸雨的微观机理进行了理论研究. 对反应势能面上的各驻点进行几何构型全优化. 振动分析和IRC计算证实了中间体和过渡态的真实性和相互连接关系. 找到了7条生成SO₂的反应途径, 其中CH₃S与O直接反应得到产物CH₃和SO最容易进行; CH₃S先与O₃反应, 其产物再与O₃反应得到CH₃SO₂, CH₃SO₂最后分解得到CH₃S和SO₂较容易进行, 其它的反应较难进行.     

Oxygen Reduction on Ag(100) in Alkaline Solutions—A Theoretical Study

Silver is much more reactive to oxygen than gold; nevertheless, in alkaline solutions, the rates of oxygen reduction on both metals are similar. To explain this phenomenon, the first, rate‐determining step of oxygen reduction on Ag(100) is determined by a combination of DFT, molecular dynamics, and electrocatalysis theory. In vacuum, oxygen is adsorbed on Ag(100), but in the electrochemical environment, the adsorption energy is offset by the loss of hydration energy as the molecule approaches the surface. As a result, the first electron transfer should take place in an outer‐sphere mode. Previously, the same mechanism for oxygen reduction on Au(100) has been predicted, and these calculations have been repeated by using a more advanced version of the electrocatalysis theory discussed herein to confirm previous conclusions. The theoretical results compare well with experimental data.     

Theoretical Study of the AICI Disproportionation Reaction Mechanism on the Al(100) Surface

The surface disproportionation reaction mechanism of aluminum subchloride on the aluminum (100) surfaces has been investigated by the plane-wave density functional theory (DFT).Three kinds of possible reaction mechanism of AlCl disproportionation reaction on the aluminum (100)surfaces have been taken into account. The structures of reactants and products have been optimized, transition states have been confirmed and activation energies have been calculated. The adsorption energy of reactants and desorption energy of products have been determined. All of these have been employed to confirm the reaction mechanism and the rate determining step of AlCl disproportionation reaction on the aluminum (100) surfaces.     

Cationic Gold(II) Complexes: Experimental and Theoretical Study**

Gold(II) complexes are rare, and their application to the catalysis of chemical transformations is underexplored. The reason is their easy oxidation or reduction to more stable gold(III) or gold(I) complexes, respectively. We explored the thermodynamics of the formation of [Au^II(L)(X)]⁺ complexes (L=ligand, X=halogen) from the corresponding gold(III) precursors and investigated their stability and spectral properties in the IR and visible range in the gas phase. The results show that the best ancillary ligands L for stabilizing gaseous [Au^II(L)(X)]⁺ complexes are bidentate and tridentate ligands with nitrogen donor atoms. The electronic structure and spectral properties of the investigated gold(II) complexes were correlated with quantum chemical calculations. The results show that the molecular and electronic structure of the gold(II) complexes as well as their spectroscopic properties are very similar to those of analogous stable copper(II) complexes.     

Theoretical Study of the AlCl Disproportionation Reaction Mechanism on the Al(100) Surface

The surface disproportionation reaction mechanism of aluminum subchloride on the aluminum (100) surfaces has been investigated by the plane-wave density functional theory (DFT).Three kinds of possible reaction mechanism of AlCl disproportionation reaction on the aluminum (100) surfaces have been taken into account.The structures of reactants and products have been optimized,transition states have been confirmed and activation energies have been calculated.The adsorption energy of reactants and desorption energy of products have been determined.All of these have been employed to confirm the reaction mechanism and the rate determining step of AlCl disproportionation reaction on the aluminum (100) surfaces.     

Exciton Migration in Conjugated Dendrimers: A Joint Experimental and Theoretical Study

We report a joint experimental and theoretical investigation of exciton diffusion in phenyl‐cored thiophene dendrimers. Experimental exciton diffusion lengths of the dendrimers vary between 8 and 17 nm, increasing with the size of the dendrimer. A theoretical methodology is developed to estimate exciton diffusion lengths for conjugated small molecules in a simulated amorphous film. The theoretical approach exploits Fermi’s Golden Rule to estimate the energy transfer rates for a large ensemble of bimolecular complexes in random relative orientations. Utilization of Poisson’s equation in the evaluation of the Coulomb integral leads to very efficient calculation of excitonic couplings between the donor and the acceptor chromophores. Electronic coupling calculations with delocalized transition densities revealed efficient coupling pathways in the bulk of the material, but do not result in strong couplings between the chromophores which are calculated for more localized transition densities. The molecular structures of dendrimers seem to be playing a significant role in the magnitude of electronic coupling between chromophores. Simulated diffusion lengths correlate well with the experimental data. The chemical structure of the chromophore, the shape of the transition densities and the exciton lifetime are found to be the most important factors in determining the size of the exciton diffusion length in amorphous films of conjugated materials.     

Diamond: Electronic Ground State of Carbon at Temperatures Approaching 0 K

The relative stability of graphite and diamond is revisited with hybrid density functional theory calculations. The electronic energy of diamond is computed to be more negative by 1.1 kJ mol^?1 than that of graphite at T=0 K and in the absence of external pressure. Graphite gains thermodynamic stability over diamond at 298 K only because of the differences in the zero‐point energy, specific heat, and entropy terms for both polymorphs.     

Theoretical Study of the Structure, Mechanism of Detonation Initiation and Stability of Transition Metal Carbohydrazide Nitrates

The geometric structure, mechanism of detonation initiation and stability of transition metal carbohydrazide （CHZ） nitrates are investigated via density functional theory. The obtained results show that the Heyd-Scuseria-Ernzerhof （HSE） functional yields the most accurate geometry. The initiating reaction of detonation in [Mn（CHZ）3]（NO3）2 and [Zn（CHZ）3]（NO3）2 is the formation of NO3 radicals. The calculated heat of formation and energy gap predict that the Mn and Zn complexes, which have the half-filled （3d5） and full-filled （3d10） electron configurations for the transition metal ions, respectively are more stable than the Co, Ni and Cu complexes. This indicates that the electron configuration of transition metal ion plays an important role in the stabilities of these energetic complexes.     

Theoretical Study of Geometric Structures for Ground-state Al_nC（n=2-7） Clusters

With the aid of the molecular orbital DMol3 program,the energetics and electronic structures of several AlnC(n = 2-7) configurations have been searched and calculated by improved minimum energy paths(MEPs) by setting "imaging product".A new high symmetry,supervalence isomer of Al5C cluster,i.e.,D5h-Al5C,at the local minimum in the MEPs is detected.Several parameters,such as binding energy,HOMO-LUMO energy gap,vertical electron detachment energy and electron affinity energy,are calculated to characterize and evaluate the stability of three Al5C configurations,i.e.,D5h-Al5C,Cs-Al5C and C1-Al5C.The results show that the D5h-Al5C cluster is the ground state structure instead of Cs-Al5C.Due to the formation of many central σ bonds after polymerizing for D5h-Al5C,the decrease of the energy for HOMO orbit results in more territory for HOMO electrons of dislocation effect,then the energy difference between HOMO and LUMO is increasing to enhance the stability of molecules to produce such supervalence structure of Al5C cluster.The configuration evolution between D5h-Al5C,Cs-Al5C and C1-Al5C and the synthesis preference in the mode of Al5 + C → Al5C reveals that the Cs-Al5C and C1-Al5C con-figurations are permissive to coexist with D5h-Al5C structure in energetics.     

Synthesis,Structure, and Theoretical Study of Trifluoromethyl Derivatives of C84(22) Fullerene

Trifluoromethylation of higher fullerene mixtures with CF₃I was performed in ampoules at 400 to 420 and 550 to 560 °C. HPLC separation followed by crystal growth and X‐ray diffraction studies allowed the structure elucidation of nine CF₃ derivatives of D₂‐C₈₄ (isomer 22). Molecular structures of two isomers of C₈₄(22)(CF₃)₁₂, two isomers of C₈₄(22)(CF₃)₁₄, four isomers of C₈₄(22)(CF₃)₁₆, and one isomer of C₈₄(22)(CF₃)₂₀ were discussed in terms of their addition patterns and relative formation energies. DFT calculations were also used to predict the most stable molecular structures of lower CF₃ derivatives, C₈₄(22)(CF₃)_2–10. It was found that the addition of CF₃ groups to C₈₄(22) is governed by two rules: additions can only occur at para positions of C₆(CF₃)₂ hexagons and no additions can occur at triple‐hexagon‐junction positions on the fullerene cage.     

Synthesis,Structure, and Theoretical Study of Trifluoromethyl Derivatives of C84(23) Fullerene

Trifluoromethylation of a higher fullerene mixture with CF₃I was performed in ampoules at 550 °C. HPLC separation followed by crystal growth and X‐ray diffraction study resulted in the structure elucidation of nine CF₃ derivatives of D_2d‐C₈₄ (isomer 23). The molecular structures of C₈₄(23)(CF₃)₄, C₈₄(23)(CF₃)₈, C₈₄(23)(CF₃)₁₀, C₈₄(23)(CF₃)₁₂, two isomers of C₈₄(23)(CF₃)₁₄, two isomers of C₈₄(23)(CF₃)₁₆, and C₈₄(23)(CF₃)₁₈ were discussed in terms of their addition patterns and the relative formation energies. Extensive theoretical DFT calculations were performed to identify the most stable molecular structures. It was found that the addition of CF₃ groups to the C₈₄(23) fullerene is governed by two main rules: no additions in positions of triple hexagon junctions and predominantly para additions in C₆(CF₃)₂ hexagons on the fullerene cage. The only exception with an isolated CF₃ group in C₈₄(23)(CF₃)₁₂ is discussed in more detail.     

Growth Mechanism and Chemical Bonding in Scandium‐Doped Copper Clusters: Experimental and Theoretical Study in Concert

Size matters! The electronic structure and size‐dependent stability of neutral and cationic scandium‐doped copper clusters have been investigated by mass spectrometric studies (for the cations) and also quantum chemical computations. The proposed reaction paths ultimately lead to the most stable Frank–Kasper‐shaped Cu₁₆Sc⁺ cluster (shown here), which could be the germ of a new crystallization process.

     

反式-双(二甲基苯膦)铂配合物二阶非线性光学性质的密度泛函理论研究

采用密度泛函理论B3LYP方法,在6-31G(d)的水平上对两种反式-双(二甲基苯膦)铂配合物的几何构型进行优化,在获得稳定构型基础上,利用TD-B3LYP方法得到体系的UV-Vis吸收光谱,并用有限场(FF/B3LYP)方法探讨体系的二阶非线性光学性质(NLO).结果表明,此类铂配合物具有较大的二阶极化率,以及在可见光范围内透明等优点,是具有很好应用前景的非线性光学材料.     

Paramagnetic NMR Shifts for Saddle-Shaped Five-Coordinate Iron(III) Porphyrin Complexes with Intermediate-Spin Structure

Calculable results: Complex density functional calculations and spin distribution analyses have been performed for planar and saddled iron(III) porphyrin complexes. The spin populations and the extent of the interactions between the metal and the porphyrin orbitals were determined, which can explain the large change of meso-carbon atom chemical shifts observed for different porphyrin ligands.     

Theoretical Study of α‐V2O5‐Based Double‐Wall Nanotubes

First‐principles calculations of the atomic and electronic structure of double‐wall nanotubes (DWNTs) of α‐V₂O₅ are performed. Relaxation of the DWNT structure leads to the formation of two types of local regions: 1) bulk‐type regions and 2) puckering regions. Calculated total density of states (DOS) of DWNTs considerably differ from that of single‐wall nanotubes and the single layer, as well as from the DOS of the bulk and double layer. Small shoulders that appear on edges of valence and conduction bands result in a considerable decrease in the band gaps of the DWNTs (up to 1 eV relative to the single‐layer gaps). The main reason for this effect is the shift of the inner‐ and outer‐wall DOS in opposite directions on the energetic scale. The electron density corresponding to shoulders at the conduction‐band edges is localized on vanadium atoms of the bulk‐type regions, whereas the electron density corresponding to shoulders at the valence‐band edges belongs to oxygen atoms of both regions.