Density Functional Calculations of C–NO_2 Bond Dissociation Energies for Nitroalkanes Molecules

Bond dissociation energies for the removal of nitrogen dioxide group in some nit- roalkane energetic materials have been calculated by using the three hybrid density functional theory (DFT) methods B3LYP, B3PW91 and B3P86 with 6-31g** and 6-311g** basis sets. The computed BDEs have been compared with the available experimental results. It is found that the B3P86 method with 6-31g** and 6-311g** basis sets can obtain satisfactory bond dissociation energies (BDEs), which are in extraordinary agreement with the experimental data. Considering the smaller mean absolute deviation and maximum difference, the reliable B3P86/6-311g** method was recommended to compute the BDEs for the removal of nitrogen dioxide group in the nitroalkane energetic materials. Using the method, the BDEs of 8 other nitroalkane energetic materials have been calculated and the maximum difference from experimental value is 1.76 kcal·mol-1 (for the BDE of tC4H9–NO2), which further proves the reliability of B3P86/6-311g** method. In addition, it is noted that the BDEs of C–NO2 bond change slightly for main chain nitroalkane compounds with the maximum difference of only 3.43 kcal mol-1.     

Density Functional Theory Calculations of 95Mo NMR Parameters in Solid‐State Compounds

The application of periodic density functional theory‐based methods to the calculation of ⁹⁵Mo electric field gradient (EFG) and chemical shift (CS) tensors in solid‐state molybdenum compounds is presented. Calculations of EFG tensors are performed using the projector augmented‐wave (PAW) method. Comparison of the results with those obtained using the augmented plane wave + local orbitals (APW+lo) method and with available experimental values shows the reliability of the approach for ⁹⁵Mo EFG tensor calculation. CS tensors are calculated using the recently developed gauge‐including projector augmented‐wave (GIPAW) method. This work is the first application of the GIPAW method to a 4d transition‐metal nucleus. The effects of ultra‐soft pseudo‐potential parameters, exchange‐correlation functionals and structural parameters are precisely examined. Comparison with experimental results allows the validation of this computational formalism.     

Vibrational Spectra and Density Functional Theory Calculations of Metallotriphenylcorroles

The infrared absorption and Raman scattering spectra were measured for the metallotriph-enylcorroles (MTPCs, M=Cu, Co, Ni, Mn). The ground-state structures and vibrational spectra of MTPCs have been calculated with the density functional theory. The observedRaman and IR bands have been assigned based on the calculation results. Due to the symmetry lowering, the vibrational spectra of MTPCs are much more complex than metal-loporphyrins, and several skeletal modes are found strongly coupled to the phenyl vibrations.The relationship between the Raman/IR frequencies and the structures of TPC ring is in-vestigated. It is found that the vibrations involving the C^I_αC^I_α stretch and C_αC_mstretch are sensitive to the size of corrole core. In particular, the frequency of υ₅, which is assigned to C^I_αC^I_α stretch in coupling with the C_αC_m symmetric stretch, increases linearly with the decrease of the corrole core-sizes and may be used as a mark band to evaluate the structural change of the metallocorroles.     

Studies on Optical Properties of Si220 Nanoclusters via Time-dependent Density Functional Theory Calculations

The optical properties of bare and hydrogen passivated Si₂₂₀ nanoclusters(NCs) in four typical motifs(i.e., bulk-like, onion-like, bucky-diamond and icosahedral motifs) were studied via time-dependent density functional theory(TD-DFT) calculations. The calculation results show that there is a significant blue shift in the optical absorption spectra when the Si NCs are passivated with hydrogen. A strong absorption peak in the visible light region appears for the hydrogenated bulk-like, onion-like and bucky-diamond Si NCs.     

Ca1-xPrxFeO3催化热解甘蔗渣木质素制备酚类化合物

采用溶胶-凝胶法合成了一系列镨掺杂的铁酸钙氧化物(Ca_1-xPr_xFeO₃, 简称CPF-x), 优化了其焙烧机制, 研究了其对甘蔗渣木质素(BL)的催化热解作用, 考察了其再生性能. 研究结果表明, CPF-x适宜的合成及焙烧参数分别为: x=0.5, 焙烧温度为800 ℃, 焙烧时间为6 h, 在该条件下得到的CPF-0.5-800-6呈立方晶相, 为疏松多孔结构; 掺杂Pr后, 其比表面积提高了近3倍. CPF-0.5-800-6对BL催化热解最佳工艺参数为: m(CPF-0.5-800-6)∶m(BL)=1∶3, 热解温度为650 ℃, 液相收率最大可达20.73%, 其中主要产物为紫丁香酚类、 苯酚类及愈创木酚类, 其总选择性为63.21%. 以CPF-0.5-800-6为催化剂, 紫丁香酚类化合物选择性由20.60%增大到29.59%, 实现了提高BL催化热解中某种单酚化合物的选择性. CPF-0.5-800-6经5次催化热解-再生循环反应后, 仍具有良好的反应活性和结构稳定性.     

并五苯分子电荷注入导致自旋极化的密度泛函理论研究

用密度泛函理论研究了不带自旋的空穴注入并五苯后体系的自旋相关特性. 电荷注入后并五苯分子中存在自发自旋极化行为. 当注入电荷量达一定程度,分子磁矩随注入电荷量的增加呈线性增长,最大磁矩可达1μB. 注入电荷和并五苯分子的相互作用导致分子体系结构发生变化,同时电荷密度分布及自旋密度分布也发生了变化. 注入电荷先填充自旋劈裂的碳原子pz轨道.     

Modeling Photovoltaic Performances of BTBPD-PC61BM System via Density Functional Theory Calculations

Designing and fabricating high-performance photovoltaic devices have remained a major challenge in organic solar cell technologies.In this work,the photovoltaic performances of BTBPD-PC₆₁BM system were theoretically investigated by means of density functional theory calculations coupled with the Marcus charge transfer model in order to seek novel photovoltaic systems.Moreover,the hole-transfer properties of BTBPD thin-film were also studied by an amorphous cell with 100 BTBPD molecules.Results revealed that the BTBPDPC₆₁BM system possessed a middle-sized open-circuit voltage of 0.70 V,large short-circuit current density of 16.874 mA/cm²,large fill factor of 0.846,and high power conversion efficiency of 10%.With the Marcus model,the charge-dissociation rate constant was predicted to be as fast as 3.079×10¹³ s^-1 in the BTBPD-PC₆₁BM interface,which was as 3-5 orders of magnitude large as the decay (radiative and non-radiative) rate constant (10⁸-10¹⁰ s^-1),indicating very high charge-dissociation efficiency (～100%) in the BTBPD-PC₆₁BM system.Furthermore,by the molecular dynamics simulation,the hole mobility for BTBPD thin-film was predicted to be as high as 3.970×10^-3 cm²V^-1s^-1,which can be attributed to its tight packing in solid state.     

菱形石墨炔薄膜He分离特性的密度泛函理论研究

氦气在科学和工业等领域中都具有不可替代的作用,其主要存在于天然气中。如何高效地从天然气中分离氦气显得至关重要。本文基于密度泛函理论(DFT)方法系统地探究了菱形石墨炔(rhombic-graphyne,R-GY)分离膜对He和其他天然气组分(Ne、Ar、CO_2、N_2和CH_4)的吸附、选择和渗透性能。结果表明,R-GY作为He分离膜可同时满足高选择性和高渗透率的要求。常温下,R-GY薄膜对He/Ne、He/CO_2、He/N_2、He/Ar和He/CH_4的选择性可分别达到2?10~7、3?10~(20)、9?10~(26)、7?10~(37)和5?10~(51),即使在600 K时仍可保持较高水平。此外,由于较低的扩散能垒,He穿透R-GY薄膜的渗透率在常温下可达到10~(-6) mol·m~(-2)·s~(-1)·Pa~(-1),高出工业标准近3个数量级;而其他气体组分在常温下的渗透率仅为10~(-58)-10~(-14) mol·m~(-2)·s~(-1)·Pa~(-1),气体无法渗透R-GY薄膜。     

中性团簇(CeO_2)_m(m=1～3)活化甲烷C—H的密度泛函理论计算

采用密度泛函理论(DFT)计算了CH4在电中性(Ce O2)m(m=1~3)团簇上的活化情况,并对其机理进行了探讨.计算结果表明,甲烷C—H键在团簇上的活化为亲核加成模式,电子由团簇流向甲烷C—H反键轨道,使甲烷C—H键削弱而得以活化,反应的过渡态为四中心结构.团簇的桥氧位活化甲烷C—H键的活性大于端氧位,而三重桥氧位的活性高于二重桥氧位.团簇中作用位点Ce和O原子的电荷布居与其活化甲烷C—H的能力密切相关.溶剂的存在不仅降低了甲烷C—H活化自由能垒,而且使与甲烷作用的团簇各位点的活性差异缩小.     

CaZr1-xFexO3催化热解甘蔗渣木质素制备酚类化合物

采用固相反应法制备了一系列钙钛矿型混合离子电子导体CaZr_1-xFe_xO₃(CZFO-x, x=0, 0.2, 0.4, 0.6, 0.8, 1.0). 通过X射线衍射(XRD)、 扫描电子显微镜(SEM)及X射线光电子能谱(XPS)对其晶型、 形貌和金属赋存价态进行了表征. 采用热重分析仪(TG)测试了其催化苷蔗渣木质素(BL)热解性能, 并采用固定床微型反应器对其催化热解BL制备酚类化合物性能进行了评价, 利用气相色谱/质谱(GC/MS)对BL催化热解的气相和液相产物进行分析. 研究结果表明, CZFO-x呈粒状或层状致密结构, 随着Fe掺杂量的增加, 其特征衍射峰强度增大, 且衍射峰位置向大角度偏移, 晶胞体积及晶粒尺寸减小. 固定床反应结果显示, 在CaZr_0.8Fe_0.2O₃(CZFO-0.2)催化下, BL热解液相产物收率可达23.71%, 其中酚类化合物主要包括苯酚类、 愈创木基类、 邻苯二酚类和紫丁香基类, 其选择性分别为35.19%, 6.18%, 10.68%和14.21%, 其余产物为苯类和甲氧基芳香化合物. 反应后催化剂经氧化再生后, 仍然具有较高的催化活性和结构稳定性. 对BL催化热解气体产物进行分析发现, CZFO-0.2促进了芳香烃烷基侧链的断裂, 致使气相产物组成中C_mH_n和CH₄含量增加.     

Ru掺杂对Fe催化剂上酚类化合物加氢脱氧影响的密度泛函理论研究北大核心CSCD

采用密度泛函理论(DFT)计算研究了苯酚、邻甲酚、愈创木酚在不同结构Ru-Fe(211)表面上吸附活化性能和加氢脱氧反应路径.结果表明,Ru掺杂能促进H2分子在Fe(211)表面上解离,提高加氢脱氧反应速率.酚类在1Ru_(ads)-Fe(211)表面上吸附比在1Ru_(sub)-Fe(211)表面上更稳定,苯酚和邻甲酚脱羟基步骤能垒分别降低0.13和0.28 eV,有利于生成芳烃.愈创木酚在1Ru_(sub)-Fe(211)表面上加氢脱氧优势路径是先脱甲氧基生成苯酚,苯酚再加氢脱氧生成产物苯(速控步骤能垒1.16 eV);而在1Ru_(ads)-Fe(211)表面上愈创木酚先脱羟基再脱甲基生成苯酚的路径更具有动力学优势(速控步骤能垒1.21 eV).计算结果表明Ru掺杂方式影响Fe催化剂对酚反应分子的吸附稳定性以及加氢脱氧反应路径和性能.与1Ru掺杂Fe(211)催化剂相比,增加Ru原子数形成4Ru_(ads)-Fe(211),能够进一步提高酚类反应物的吸附强度,但导致加氢脱氧反应能垒升高.因此,在Fe催化剂上以表面吸附的形式掺杂少量贵金属Ru更利于酚类加氢脱氧生成芳烃.     

Density Functional Theory Calculations on Oxidative CC Bond Cleavage and NO Bond Formation of [RuII(bpy)2(diamine)]2+ via Reactive Ruthenium Imide Intermediates

DFT calculations are performed on [Ru^II(bpy)₂(tmen)]²⁺ ( M1 , tmen=2,3‐dimethyl‐2,3‐butanediamine) and [Ru^II(bpy)₂(heda)]²⁺ ( M2 , heda=2,5‐dimethyl‐2,5‐hexanediamine), and on the oxidation reactions of M1 to give the C?C bond cleavage product [Ru^II(bpy)₂(NH=CMe₂)₂]²⁺ ( M3 ) and the N?O bond formation product [Ru^II(bpy)₂(ONCMe₂CMe₂NO)]²⁺ ( M4 ). The calculated geometrical parameters and oxidation potentials are in good agreement with the experimental data. As revealed by the DFT calculations, [Ru^II(bpy)₂(tmen)]²⁺ ( M1 ) can undergo oxidative deprotonation to generate Ru‐bis(imide) [Ru(bpy)₂(tmen‐4 H)]⁺ ( A ) or Ru‐imide/amide [Ru(bpy)₂(tmen‐3 H)]²⁺ ( A′ ) intermediates. Both A and A′ are prone to C?C bond cleavage, with low reaction barriers (ΔG^≠) of 6.8 and 2.9 kcal mol^?1 for their doublet spin states ² A and ² A′ , respectively. The calculated reaction barrier for the nucleophilic attack of water molecules on ² A′ is relatively high (14.2 kcal mol^?1). These calculation results are in agreement with the formation of the Ru^II‐bis(imine) complex M3 from the electrochemical oxidation of M1 in aqueous solution. The oxidation of M1 with Ce^IV in aqueous solution to afford the Ru^II‐dinitrosoalkane complex M4 is proposed to proceed by attack of the cerium oxidant on the ruthenium imide intermediate. The findings of ESI‐MS experiments are consistent with the generation of a ruthenium imide intermediate in the course of the oxidation.     

DFT法研究3-羟基丙烯醛的双键旋转异构反应机理

利用密度泛函理论(DFT)分别在B3LYP/6-31G**和B3LYP/6-311＋＋G**的计算水平上优化了基态3-羟基丙烯醛分子在双键旋转异构反应过程中的平衡态以及过渡态的几何构型，分析了反应过程中键参数的变化，计算了该反应的内禀反应坐标(IRC)，发现在重排反应途径上存在一个四元环骨架的中间体.通过振动分析对平衡态和过渡态进行了确认，并得到了零点能.计算结果表明，基态3-羟基丙烯醛分子的双键旋转异构反应经过两步完成，第一步反应位垒稍高，第二步反应位垒较低，存在着发生重排反应的可能性.     

Adsorption of Carbamazepine in All-Silica Zeolites Studied with Density Functional Theory Calculations**

The anticonvulsant drug carbamazepine (−) is an emerging contaminant of considerable concern due to its hazard potential and environmental persistence. Previous experimental studies proposed hydrophobic zeolites as promising adsorbents for the removal of carbamazepine from water, but only a few framework types were considered in those investigations. In the present work, electronic structure calculations based on dispersion-corrected density functional theory (DFT) were used to study the adsorption of CBZ in eleven all-silica zeolites having different pore sizes and connectivities of the pore system (AFI, ATS, BEA, CFI, DON, FAU, IFR, ISV, MOR, SFH, SSF framework types). It was found that some zeolites with one-dimensional channels formed by twelve-membered rings (IFR, AFI) exhibit the highest affinity towards CBZ. A “good fit” of CBZ into the zeolite pores that maximizes dispersion interactions was identified as the dominant factor determining the interaction strength. Further calculations addressed the role of temperature (for selected systems) and of guest-guest interactions between coadsorbed CBZ molecules. In addition to predicting zeolite frameworks of particular interest as materials for selective CBZ removal, the calculations presented here also contribute to the atomic-level understanding of the interaction of functional organic molecules with all-silica zeolites.     

Vibrational Spectra and Density Functional Theory Calculations of Metallo-tetra-(tert-butyl)-tetra-azaporphyrines

The infrared absorption and 514.5 nm excited Raman spectra were measured for the metallo-tetra-(tert-butyl)-tetraazaporphyrin (MT(tBu)TAP, M=Cu, Co, Ni, Zn). The ground-state structures and vibrational spectra of MT(tBu)TAPs have been calculated at the B3LYP level of theory. The observed Raman and IR bands have been assigned based on the calculation results and by comparing with the normal metalloporphyrins. The relationship between the Raman/IR frequencies and the structures of TAP ring was investigated. The results show that the frequencies of C_βC_β′ stretch (A_g), asymmetric C_αN_m stretch (A_g), and symmetric C_αN_m stretch (B_g) modes increase linearly with the decrease of the core-sizes of TAP ring.Among the three modes, the later two are more sensitive to the core-size change.     

羰基镍簇Ni(CO)n(n=1-4)的结构和Ni-CO键解离性质的密度泛函理论研究

在密度泛函理论框架下, 应用不同泛函计算了配合物Ni(CO)n(n=1~4)的平衡几何构型和振动频率. 考察了泛函和基组重叠误差对预测Ni—CO键解离能的影响. 计算结果表明, 用杂化泛函能得到与实验一致的优化几何构型和较合理的振动频率. 对Ni(CO)n(n=2~4)体系, 用“纯”泛函, 如BP86和BPW91, 可得到与CCSD(T)更符合、 并与实验值接近的解离能. 当解离产物出现单个金属原子或离子(如金属羰基配合物的完全解离)时, BSSE校正项的计算中应保持金属部分的电子结构一致. 只有考虑配体基组和不考虑配体基组两种情况下金属的电子构型与配合物中金属的构型一致时, 才能得到合理的BSSE校正, 从而预测合理的解离能.     

Substituent Effects on Site Selectivity (C=C vs C=N) in Heterocumulene-Heterodiene [4 + 2] Cycloadditions: Density Functional and Semiempirical AM1 Molecular Orbital Calculations

The effect of substituents on the site selectivity (C=C vs C=N) in the [4 + 2] cycloaddition between heterocumulenes (ketene imines) 2a-g with heterodienes (acroleines 9a-n and 4-acylfuran-2,3-diones 1a-d) is treated by semiempirical AM1 molecular orbital and density functional calculations using Becke's three-parameter hybrid method (B3LYP/6-31G). For some reactions calculations were also done at the B3LYP/6-31+G level of theory. For reaction of the oxa 1,3-dienes with ketene imines unsubstituted at the terminal carbon invariably addition across the C=C heterocumulene double bond has a lower activation energy than addition across the C=N double bond. Substitution of methyl or especially phenyl groups at the ketene imine C-terminus leads to a reversal of the respective activation energies. Incorporation of the oxa 1,3-diene system into the heterocyclic dione 1 substantially enhances the reactivity ( approximately 10 kcal mol(-1) lower activation energies) as compared to similarly substituted acroleins. At the DFT level of theory all reactions are found to proceed via a concerted asynchronous mechanism.     

Density Functional Studies of the Reaction of Ytterbium Monocation with Fluoromethane：C—F Bond Activation and Electron—Transfer Reactivity

The potential energy surface and reaction mechanism corresponding to the reaction of ytterbium monocation with fluoromethane, which represents a prototype of the activation of C-F bond in fluorohydrocarbons by bare lanthanide cations, have been investigated for the first ime by using density functional theory. A direct fluorine abstraction mechanism was revcaled, and the related thermochemistry data were determined. The electron-transfer reactivity of the reaction was analyzed using the two-state model, and a strongly avoided crossing behavior on the transition state region was shown. The present results support the reaction mechanism inferred from early experimental data and the related thermochemistry data can provide a guide for further experimental researches.     

Removal of Phenolic and Lignin Compounds from Bleached Kraft Mill Effluent by Fly Ash and Sepiolite

This study aimed to remove phenolic and lignin compounds from paper mill industry (4500 m³/h) wastewaters, which is discharged to sea from a plant located in the western Turkey. As adsorbent, fly ash, raw sepiolite and heat-activated sepiolite were used. The effect of factors such as, particle size, temperature and pH on adsorption process was investigated. From kinetic studies, equilibrium time was found as 1 h for both. The kinetic data supports pseudo-second order model but shows very poor fit for pseudo-first order model. Intraparticle model also shows that there are two separate stages in sorption process, namely, external diffusion and pore diffusion. Adsorption isotherms for fly ash and activated sepiolite were obtained at two different temperatures. From experiments carried out at different pHs, it was observed that pH plays an important role in the adsorption process in removing of both lignin and phenolic compounds, providing both ionizating the compounds and modifying sorbent surfaces. It was also observed that heat-activated sepiolite is more effective than raw sepiolite and fly ash to remove these compounds. Adsorption of lignin and phenolic compounds increases with decreasing particle size. In addition, the efficiency of adsorption decreases with increasing adsorption temperature for both fly ash and untreated sepiolite.