密度泛函理论研究十二烷硫醇在Au(111)面上的吸附

采用第一性原理方法研究了十二烷硫醇(C₁₂H₂₅SH)分子在Au(111)面上未解离和解离吸附的结构、能量和吸附性质,在此基础上分析判断长链硫醇分子在Au(111)面吸附时S―H键的解离, 以及分子链长度对吸附结构和能量的影响. 计算了S原子在不同位置以不同方式吸附的系列构型, 结果表明在S―H键解离前和解离后,均存在两种可能的表面结构, 直立吸附构型和平铺吸附构型; 未解离的C₁₂H₂₅SH分子倾向于吸附在top位, 吸附能为0.35-0.38 eV; H原子解离后C₁₂H₂₅S基团倾向于吸附在bri-fcc位, 吸附能量为2.01-2.09 eV. 比较分析未解离吸附和解离吸附, 发现C₁₂H₂₅SH分子未解离吸附相较于解离吸附要稳定, 未解离吸附属于弱化学吸附.局域电子态密度和差分电荷密度分析进一步验证了S―H解离后S原子与表面之间成键的数目增加, 而且键合更强. 同时我们发现长链硫醇的吸附能量较短链硫醇的吸附能量略大, S原子与表面Au原子之间的距离略小.     

AgGa(S1-xSex)2固溶体的电子结构和光学性质

采用基于赝势平面波基组的密度泛函理论方法, 对一系列具有黄铜矿结构的AgGa(S_1-xSe_x)₂固溶体的构型、电子结构、线性和二阶非线性光学性质进行了系统研究. 结果表明, 各固溶体具有类似的能带结构, 体系带隙随x值增加而逐渐减小. 当所引入的Hartree-Fock交换项贡献为22.56%时, 对应的杂化PBE泛函得到的带隙值与实验结果相近. 固溶体的各种光学性质, 包括折射率、双折射率、反射率、吸收系数和二阶倍频系数等均随着组成的改变呈现出有规律的变化趋势, 变化范围介于AgGaS₂和AgGaSe₂二者之间. 因此, 利用固溶体光学性质的变化规律, 可从中寻找出具有特定光学性能的晶体材料.     

Changes in electronic,magnetic and bonding properties from Zr2FeH5 to Zr3FeH7 addressed from ab initio

Potential hydrogen storage ternaries Zr₃FeH₇ and Zr₂FeH₅, are studied from ab initio with the purpose of identifying changes in electronic structures and bonding properties. Cohesive energy trends: E_coh. (ZrH₂) > E_coh. (Zr₂FeH₅) > E_coh. (Zr₃FeH₇) > E_coh. (hypothetic-FeH) indicate a progressive destabilization of the binary hydride ZrH₂ through adjoined Fe so that Zr₃FeH₇ is found less cohesive than Zr₂FeH₅. From the energy volume equations of states EOS the volume increase upon hydriding the intermetallics leads to higher bulk moduli B₀ explained by the Zr/Fe–H bonding. Fe–H bond in Zr₂FeH₅ leads to annihilate magnetic polarization on Fe whereas Fe magnetic moment develops in Zr₃FeH₇ identified as ferromagnetic in the ground state. These differences in magnetic behaviors are due to the weakly ferromagnetic Fe largely affected by lattice environment, as opposed to strongly ferromagnetic Co. Hydrogenation of the binary intermetallics weakens the inter-metal bonding and favors the metal–hydrogen bonds leading to more cohesive hydrides as with respect to the pristine binaries. Charge analyses point to covalent like Fe versus ionic Zr and hydrogen charges ranging from covalent H^−0.27 to more ionic H^−0.5.     

二维金属-六亚氨基苯框架材料的气体吸附效应

利用密度泛函理论研究了气体分子(NH₃, H₂O, H₂S, NO₂)吸附在二维M₃(HIB)₂(M=Ni, Cu; HIB为六亚氨基苯)薄膜上体系的几何结构和电子结构的变化. 结果表明, 2种薄膜对气体分子的响应不同. 其中NH₃, H₂O和H₂S在M₃(HIB)₂薄膜表面的吸附较弱, 主要与薄膜的亚氨基形成氢键, 吸附能均小于-0.36 eV, 吸附对体系电子性质的影响很小. 但是 NO₂分子在薄膜表面形成化学吸附, 吸附能在-0.65~-1.72 eV范围内. 吸附NO₂分子使其电子结构发生明显改变, 如Cu₃(HIB)₂在费米能级处打开带隙, 由金属性质转变为半导体性质. 这是由于NO₂分子的p_z轨道与金属原子$d_{z}^{2}$ 轨道发生了强烈的轨道杂化. 此外, 研究发现高浓度的NO₂分子吸附能够使Ni₃(HIB)₂薄膜由非磁性变为磁性体系, 由普通金属性质变为半金属性质; 而高浓度的NO₂分子使Cu₃(HIB)₂薄膜由金属性质变为半导体性质, 薄膜电导率降低.     

Absolute configuration of Buagafuran:An experimental and theoretical electronic circular dichroism study

Buagafuran is a novel drug candidate derived from natural product.Its absolute configuration has been confirmed by electronic circular dichroism combined with modern quantum-chemical calculation using time-dependent density functional theory.The predicted UV absorbance peak is underestimated by several nanometers compared with the experimental data.The applicability of empirical rule for the C=C-C-O system in Buagafuran has also been discussed.Our results show that electronic circular dichroism could be a useful tool for the absolute configuration assignment of chiral drugs,especially for the oily or semisolid substances,whose crystal structures are impossible to obtain.     

环四甲撑四硝胺(HMX)结构和性质的DFT研究

用密度泛函理论(DFT)B3LYP方法,取6-31G基组,求得环四甲撑四硝胺分子的几何构型、电子结构、 IR谱和298～1200 K的热力学性质.全优化几何构型和电子结构均具有Ci对称性.在相邻原子之间以N-NO2键的Mulliken集居数最小,表明其间电子分布较少,预示其为热解和起爆的引发键.IR谱与实验结果良好相符.     

CuO—ZnO／Al2O3—TiO2催化剂中TiO2的结构和电子效应

采用XPS,XRD,TPR,TPD和指标反应等方法研究了TiO_2在负载型CuO-ZnO/Al_2O_3-TiO_2催化剂中所起的作用.发现TiO_2起双重作用,即结构效应和电子效应,TiO_2的结构效应主要表现为它改善了CuO在载体上的分布.TiO_2的电子效应表现为它对Cu~0具有吸电子的作用,从而削弱了Cu和S之间的吸附力,使S容易脱除.另外,部分还原形成的Ti~(3+)具有促进CuS中的Cu~(2+)还原为Cu~0的能力,TiO_2的上述效应的综合结果使催化剂的抗硫中毒性能大大增强.     

The steric and electronic effects of aliphatic fluoroalkyl groups

Ab initio calculations were performed on 18 fluorinated and unfluorinated alcohols at the B3LYP and HF levels with the 6-311G^∗∗ basis set. Molar volumes of the alcohols were computed at each level and averaged to produce a scale of relative size. From this, various isosteric replacements of potential use in drug design were suggested: ethyl by FCH₂CH₂ or HCF₂CH₂, propyl by CF₃CH₂, isopropyl by CF₃(CH₃)CH or (FCH₂)₂CH, isobutyl or t-butyl by (CF₃)₂CH, and 3-methyl-2-butyl by CF₃(CH₃)₂C. Calculation of the charge on oxygen and the Wiberg index of the CO bond allowed an electronegativity scale to be constructed for the fluoroalkyl groups. Electronegativity decreased in the order: (CF₃)₃C>(CF₃)₂CH>C₂F₅CH₂>CF₃CH₂>CH₃(CF₃)₂C>HCF₂CH₂>CF₃(CH₃)CH>(FCH₂)₂CH>FCH₂CH₂>CF₃(CH₃)₂C. This ranking agreed with literature acid dissociation data for the alcohols studied.     

Activation-induced layered structure in NiCoAl by atomic modulation for energy storage application

The surface activation of alloys favors their electrochemical interactions, ion diffusivity, and the rapid kinetics of ions and electrons, leading to the formation of self-supported layered double hydroxides (LDHs) in them. However, the formation of LDHs at different depths in the alloy upon activation, their electronic/atomic structures, and their electrochemical charge storage mechanism, have not been thoroughly explored. Herein, Ni ion-substituted CoAl alloys are prepared by arc melting and activated by KOH electrolyte, which is responsible for the modulation of the atomic configuration as confirmed by XRD. Raman depth mapping demonstrates how the LDHs vary with depth upon activation and that the octahedral and tetrahedral symmetry sites of CoO and Co₃O₄ are responsible for the formation of the layered structures of CoOOH and Co(OH)₂, respectively. The activated Ni₁₀Co₈₅Al₅ has a superior volumetric capacitance of 4.15 F/cm³ at 0.5 mA/g, which is 38.6 times that of an unactivated one, and excellent cyclic stability up to 5000 cycles, and a voltage of 0.54 V generated from a fabricated supercapacitor cell. X-ray Absorption Spectroscopy (XAS) analysis indicates greater charge transfer by Co than by Ni and the modulation of the local atomic structures facilitates electrochemical charge storage in Ni₁₀Co₈₅Al₅. This work presents an easy route for the development of advanced LDHs, and the mechanism of electrochemical charge storage in them.