Capture and separation of CO2 on BC3 nanosheets: A DFT study

In order to reduce the greenhouse effect caused by the rapid increase of CO₂ concentration in the atmosphere, it is necessary to develop more efficient, controllable, and highly sensitive adsorbing materials. In this study, the adsorption behavior of CO₂ on BC₃ nanosheets under an external electric field was explored based on density functional theory (DFT). It was found that CO₂ experienced a transition from physisorption to chemisorption in the electric field range of 0.0060-0.0065 a.u.. In addition, the adsorption/desorption of CO₂ is reversible and can be precisely controlled by switching on/off at the electric field of 0.0065 a.u.. The selective adsorption of CO₂/H₂/CH₄ by BC₃ can also be used to realize gas separation and purification under different electric fields. This study highlighted the potential application of BC₃ nanosheets as a high-performance, controllable material for CO₂ capture, regeneration, and separation in an electric field.     

A DFT study on structural stability and electronic property of VIIIB transition metal-doped carbon nanocaps

Carbon nanocap (CNC) was selected for the systems doped with VIIIB transition metal (TM) atoms. The geometrical structures and electronic properties of TM-doped CNCs were calculated using the density functional theory method. It was found that TM atoms can interact with CNC to form TM–CNC complexes, which corresponded with the large partial charge transfer. All of molecular orbitals of TM–CNC complexes were localized in vicinity doping site. The density of states of these TM-doped CNCs were exhibited mostly metallic or narrow–gap semiconductor.     

Revisiting the reduction of indoles by hydroboranes: A combined experimental and computational study

A combined experimental and density functional computational study was used to probe the mechanism for the reduction of indoles using simple borane BH₃·DMS (DMS?=?dimethyl sulfide). Experimental and computational studies all steer to the formation of the reduced species 1-BH₂-indolines as the resting state for this reaction, as opposed to the historically presumed formation of the unreduced 1-BH₂-indoles, before the addition of a proton source to form the final product indolines. Furthermore, it was observed that molecular H₂ was generated and consumed in the reaction. Computations put forward hydroboration followed by protodeborylation as the very reasonable mechanistic route for the formation of experimentally observed major intermediate 1-BH₂ indolines. For the H₂ consumption in the reaction, computations suggest the frustrated Lewis pair-type heterolytic splitting of H₂ by a bis(3-indolinyl)borane intermediate.     

Structural,mechanical, electronic,optical properties and effective masses of CuMO2 (M = Sc,Y, La) compounds: First-principles calculations

The structural, elastic, mechanical, electronic, optical properties and effective masses of CuM_IIIBO₂ (M_IIIB = Sc, Y, La) compounds have been investigated by the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory under local density approximation. The equilibrium structural parameters are in good agreement with previous experimental and theoretical data. To our knowledge, there are no available data of elastic constants for comparison. The bulk, shear and Young's modulus, ratio of B/G, Poisson's ratio and Lamé's constants of CuM_IIIBO₂ have been studied. The electronic structures of CuM_IIIBO₂ are consistent with other calculations. The population analysis, charge densities and effective masses have been shown and analyzed. The imaginary and real parts of the dielectric function, refractive index and extinction coefficient of CuM_IIIBO₂ are calculated. The interband transitions to absorption of CuM_IIIBO₂ have been analyzed.     

First-principles study of structural,elastic, electronic and vibrational properties of BiCoO3

We used density functional theory (DFT) to study the structural, elastic, electronic, and lattice dynamical properties of tetragonal BiCoO₃ applying the “norm-conserving” pseudopotentials within the local spin density approximation (LSDA). The calculated equilibrium lattice parameters and atomic displacements are in agreement with the available experimental and theoretical results. Moreover, the structural stability of tetragonal BiCoO₃ were confirmed by the calculated elastic constants. In addition, the elastic properties of polycrystalline aggregates including bulk, shear and Young's moduli, and Poisson's ratio are also determined. The electronic band structure, total and partial density of states (DOS and PDOS) with ferromagnetic spin configuration are obtained. The results show that tetragonal BiCoO₃ has an indirect band gap with both up- and down-spin configurations and its bonding behavior is of covalent nature. We compute Born effective charge (BEC) which is found to be quite anisotropic of Bi, Co and O atoms. The infrared and Raman active phonon mode frequencies at the Г point are found. The phonon dispersion curves exhibit imaginary frequencies which lead from the high-symmetry tetragonal phase to low-symmetry rhombohedral phase in BiCoO₃. The six independent elastic constants, including bulk, shear and Young's moduli, and Poisson's ratio, complete BEC tensor and phonon dispersion relations in tetragonal BiCoO₃ are predicted for the first time. Results of the calculations are compared with the existing experimental and theoretical data.     

密度泛函理论计算研究表面应力对钯催化乙炔选择性加氢活性与选择性的影响（英文）

在石油催化裂解过程中,除了生成乙烯、丙烯及丁烯等烯烃,还会产生部分炔烃.目前工业上通常采用炔烃选择性加氢转化为对应的单烯烃,以除去其中炔烃.由于产品烯烃中的炔烃等杂质含量需极低,这就对用于加氢催化剂的活性和选择性提出了很高的要求,即催化剂需要选择性吸附炔烃并加氢,而不损失其中的烯烃.经过前期大量的基础研究工作,目前工业中炔烃选择性加氢应用最广泛的催化剂是负载型钯基催化剂.然而,单独的钯金属选择性并不理想,因而对其选择性以及活性进行调控成为了当前关注的研究课题.本文采用密度泛函理论计算结合微观反应动力学模拟手段,研究了钯金属表面应力存在条件下的活性与选择性,以及形成次表层物种的可能性和形成后的活性与选择性.研究发现,改变钯金属的晶格参数与表面应力,反应物、表面反应中间体和产物的吸附能都会产生相应的变化,且吸附能与晶格参数的变化存在线性关系,晶格参数越大,吸附越强.利用表面反应过渡态能量与初始态能量之间的线性关系,相应的乙炔加氢生成乙烯的反应速率可以通过微观反应动力学模拟得到.结果显示,不同晶格参数的钯催化剂催化乙炔加氢生成乙烯的反应活性位于相应火山型曲线的强吸附侧,即减弱乙炔和氢的吸附强度可提高乙烯的生成速率.在此基础上,本文研究了不同表面应力的钯催化剂在次表面吸附不同覆盖度碳原子和氢原子的情况,发现晶格参数越大越有利于碳原子和氢原子在次表面的吸附.同时,研究发现在次表面碳掺杂的条件下,不同表面应力条件下的钯催化剂的活性均有所增强.此外,由于乙烯在所有研究的钯催化剂表面脱附比进一步加氢容易,因而乙烯都可以选择性生成.     

The origin of the stereochemically active Pb(II) lone pair: DFT calculations on PbO and PbS

The concept of a chemically inert but stereochemically active 6s² lone pair is commonly associated with Pb(II). We have performed density functional theory calculations on PbO and PbS in both the rocksalt and litharge structures which show anion dependence of the stereochemically active lone pair. PbO is more stable in litharge while PbS is not, and adopts the symmetric rocksalt structure showing no lone pair activity. Analysis of the electron density, density of states and crystal orbital overlap populations shows that the asymmetric electron density formed by Pb(II) is a direct result of anion-cation interactions. The formation has a strong dependence on the electronic states of the anion and while oxygen has the states required for interaction with Pb 6s, sulphur does not. This explains for the first time why PbO forms distorted structures and possesses an asymmetric density and PbS forms symmetric structures with no lone pair activity. This analysis shows that distorted Pb(II) structures are not the result of chemically inert, sterically active lone pairs, but instead result from asymmetric electron densities that rely on direct electronic interaction with the coordinated anions.     

Facile Modulation of FLP Properties: A Phosphinylvinyl Grignard Reagent and Ga/P‐ and In/P2‐Based Frustrated Lewis Pairs

An Al/P‐based frustrated Lewis pair (FLP) reacted with PhMgCl by an unexpected transmetalation and formation of a phosphinylvinyl Grignard reagent. This compound is well suited for the transfer of the basic FLP component to other Lewis acidic metal atoms and allowed the generation of a Ga/P and an In/P₂ FLP. The Ga FLP showed a behavior different to that of the corresponding Al FLP, the In FLP allowed the chelating coordination of an Au atom by Au−Cl bond activation.     

取代苯甲酸羧基上H和O原子的部分电荷与Hammett常数之间的线性关系

采用密度泛函分析了取代苯甲酸中羧基上的H1原子和2个氧原子O2和O3的电荷与取代基的Hammett常数之间的线性关系. 比较了不同密度泛函和电荷计算方法B3LYP/6-311G*/(NBO, Mulliken), (BLYP, BP, PWC)/DNP/(Hirshfeld, Mulliken)对上述线性相关系数的影响. 结果表明, BLYP/DNP/Hirshfeld方法的计算精度高且计算速度快. 使用BLYP/DNP/Hirshfeld方法计算了70个取代苯甲酸的部分电荷, 发现H1, O2和O3原子的电荷与取代基Hammett常数σ_p和σ_m之间的线性相关系数可达到0.98以上, 其中O2的电荷和Hammett常数的线性相关性最好. O2的电荷值可以作为Hammett常数的替代, 用于结构性能定量分析, 也可以用于预测取代基的Hammett常数.     

The C−NO2 bond dissociation energies of some nitroaromatic compounds: DFT study

The C−NO₂ bond dissociation energies in nitrobenzene; 3-amino-nitrobenze; 4-amino-nitrobenze; 1,3-dinitrobenzene; 1,4-dinitrobenzene; 2-methyl-nitrobenzene; 4-methyl-nitrobenzene; and 1,3,5-trinitrobenzene nitroaromatic molecules, are computed using B3LYP, B3PW91, B3P86 three-parameter hybrid Density Functional Theory (DFT) methods in conjunction with 6-31G^** basis set. By comparing the computed energies and experimental ones, it is found that B3P86/6-31G^** is not capable of predicting the satisfactory bond dissociation energy (BDE). The BDEs computed with both B3LYP/6-31G^** and B3PW91/6-31G^** for the nitroaromatic molecules are closer to the experimental ones than those obtained with B3P86/6-31G^**. But, when compared with the experimental one, the BDE from the B3LYP/6-31G^** has the maximum deviation, which is completely outside our desired target accuracy for chemical predictions (less than 2.00 kcal mol⁻¹). Therefore, we suggest B3PW91/6-31G^** method as a reliable method of computing the BDE for removal of the nitrogen dioxide group in the nitroaromatic compounds. In addition, the C−NO₂ BDEs for 2,4,6-trinitrotoluene (TNT), triaminotrinitrobenzene (TATB), diaminotrinitrobenzene (DATB), and picramide are studied with B3PW91/6-31G^** method.     

A theoretical study on the vibrational spectra and thermodynamic properties for the nitro derivatives of phenols

The nitro derivatives of phenols are optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/6-31G* level. Their IR spectra are obtained and assigned by vibrational analysis and are reliable compared with the experimental results. Based on the frequencies scaled by 0.96 and the principle of statistic thermodynamics, the thermodynamic properties are evaluated, which are linearly related with the number of nitro and hydroxy groups as well as the temperature, obviously showing good group additivity.     

Acid-catalysed oxidative ring-opening of epoxide by DMSO. Theoretical investigation of the effect of acid catalysts and substituents

DFT studies have been carried out in order to investigate the reaction mechanism of a series of acid-catalysed oxidative ring-opening of epoxides in DMSO. The role of the acid catalyst during the oxidation of ethylene oxide has been investigated by employing three acids, namely H₃O⁺, Li⁺, and Mg²⁺. Effects of substituents on the epoxide have been investigated by including butene oxide and cyclopentene oxide as the reacting species. Stationary points have been obtained at the B3LYP/6–31++G(d,p) level of theory and the reaction barriers have been evaluated through free-energy calculations. This is the first mechanistic elucidation for such a process, involving oxidation of the epoxide ring by DMSO. The mechanism proceeds in two steps, namely a ring-opening step followed by an intramolecular proton transfer which leads to an -hydroxyketol. The results show that the second step is the energetically less favourable, a feature consistent with the harsh experimental conditions needed to obtain such products. The role of the acid catalyst is discussed and we show that use of H₃O⁺ or Mg²⁺ as an activator leads to similar results concerning the reaction energetics.Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail     

The mechanism of ethylene polymerization by nickel salicylaldiminato catalysts - Agostic interactions and their kinetic isotope effects

The ethylene polymerization reaction of a neutral nickel catalyst was studied by DFT calculations at the Becke3LYP/6-31G(d) level of theory. As in related cases a β-agostic bond stabilizes the nickel alkyl ground states. Transition states for the insertion of the olefin show a distinct α-agostic interaction, which has not been observed for late metal polymerization catalysts before. An ethylene-alkyl complex was identified as the resting state of the reaction. The overall barrier height of the reaction amounts to 17.54 kcal/mol, which slightly increases to 17.60 kcal/mol for the polymerization of deuterated ethylene. Therefore, a small positive kinetic isotope effect (k_H/k_D = 1.09) can be calculated, which is caused by the α-agostic interaction in the transition state. A comparison to other late metal based polymerization systems reveals that the ethylene coordination step of highly active catalysts is significantly lower in energy compared to catalysts which are only moderately active.     

Insight into room-temperature catalytic oxidation of NO by CrO2(110): A DFT study

The first-principles DFT calculations together with microkinetic analysis reveal the complex catalytic mechanism of low-content NO oxidation on CrO₂(110) at room temperature. It quantitatively makes clear that CrO₂(110) can exhibit considerable activity with the Mars-van-Krevelen mechanism preferred, and the nitrate species serves as the key poisoning species.     

Understanding the role of the Lewis acid catalyst on the 1,3-dipolar cycloaddition of N-benzylideneaniline N-oxide with acrolein: a DFT study

The Lewis acid (LA) catalyzed 1,3-dipolar cycloaddition of N-benzylideneaniline N-oxide with acrolein has been studied using DFT calculations. Coordination of AlCl₃ to the acrolein oxygen atom produces a drastic change in the mechanism along the more favorable meta reactive channel. The process is characterized by a strong nucleophile/electrophile interaction allowing the formation of a zwitterionic intermediate, a Michael-type addition. The subsequent ring closure constitutes the rate-determining step. The energies obtained with the inclusion of solvent effect by means of the polarizable continuum model are in good agreement with experimental findings. Analysis of the global and local electrophilicity allows to explain correctly the reactivity and regioselectivity of the LA catalyzed cycloaddition.     

Theoretical investigation of the coordination of dibenzazepine to transition-metal complexes: A DFT study

DFT calculations with full geometry optimizations have been carried out on a series of hypothetical compounds of the CpM(C₁₄NH₁₁) and (CO)₃M(C₁₄NH₁₁) (M = transition metal and C₁₄NH₁₁ = dibenzazepine ligand) type. A rationalization of the bonding in hypothetical complexes is provided. Depending on the electron count and the nature of the metal, the dibenzazepine ligand can bind to the metal through the η¹, η², η³, η⁴ , η⁵, η⁶ , or η⁷ coordination mode adopting structures of types a or b. In the investigated species, the most favored closed-shell count is 18-MVE except for the Sc and V models which prefer the 16-MVE configuration.     

Magnetic exchange behavior of a long-range Cu system through the diamagnetic Cu2 unit bridge: A DFT study

The mechanism of magnetic exchange interaction in an interesting Cu^II coordination polymer with the Cu^I₂X₂ (X = I or Br) moiety bridge is investigated by the calculations based on density functional theory combined with the broken-symmetry approach (DFT-BS). Surprisingly, different from the experiment results, the calculations reveal that the complex between the magnetic Cu^II centers has a fairly weak antiferromagnetic interaction for the long distance (∼10 Å). The analyses show of the molecular orbitals and the spin density distribution favor the very weak antiferromagnetic coupling interactions of the systems.     

Intramolecular Frustrated Lewis Pair with the Smallest Boryl Site: Reversible H2 Addition and Kinetic Analysis

Ansa‐aminoborane 1 (ortho‐TMP? C₆H₄? BH₂; TMP=2,2,6,6‐tetramethylpiperid‐1‐yl), a frustrated Lewis pair with the smallest possible Lewis acidic boryl site (? BH₂), is prepared. Although it is present in quenched forms in solution, and BH₂ represents an acidic site with reduced hydride affinity, 1 reacts with H₂ under mild conditions producing ansa‐ammonium trihydroborate 2 . The thermodynamic and kinetic features as well as the mechanism of this reaction are studied by variable‐temperature NMR spectroscopy, spin‐saturation transfer experiments, and DFT calculations, which provide comprehensive insight into the nature of 1 .