Hydrogen bond interactions in sulfamerazine: DFT study of the O-17, N-14, and H-2 electric field gradient tensors

Hydrogen bond (HB) interactions are studied in the real crystalline structure of sulfamerazine by density functional theory (DFT) calculations of the electric field gradient (EFG) tensors at the sites of O-17, N-14, and H-2 nuclei. One-molecule (single) and four-molecule (cluster) models of sulfamerazine are created by available crystal coordinates and the EFG tensors are calculated in both models to indicate the influence of HB interactions on the tensors. Directly relate to the experiments, the calculated EFG tensors are converted to the experimentally measurable nuclear quadrupole resonance (NQR) parameters, quadrupole coupling constant (qcc) and asymmetry parameter (η_Q). The evaluated NQR parameters reveal that due to contribution of the target molecule to N–HN and N–HO types of HB interactions, the EFG tensors at the sites of various nuclei are influenced from single model to the target molecule in cluster. Additionally, O2, N4, and H2 nuclei of the target molecule are significantly influenced by HB interactions, consequently, they have the major contributions to HB interactions in cluster model of sulfamerazine. The calculations are performed employing B3LYP method and 6-311++G** basis set using GAUSSIAN 98 suite of program.     

A DFT study of the CO adsorption and oxidation at ZnO surfaces and its implication for CO detection

Recently,ZnO-based gas sensors have been successfully fabricated and widely studied for their excellent sensitivity and selectivity,especially in CO detection.However,detailed explorations of their mechanisms are rather limited.Herein,aiming at clarifying the sensing mechanism,we carried out density functional theory(DFT) calculations to track down the CO adsorption and oxidation on the ZnO(101 0) and(1120) surfaces.The calculated results show that the lattice O of ZnO(1010) is more reactive than that of ZnO(1120) for CO oxidation.From the calculated energetics and structures,the main reaction product on both surfaces can be determined to be CO_2 rather than carbonate.Moreover,the surface conductivity changes during the adsorption and reaction processes of CO were also studied.For both ZnO(1010) and(1120),the conductivity would increase upon CO adsorption and decrease following CO oxidation,in consistence with the reported experimental results.This work can help understand the origins of ZnO-based sensors' performances and the development of novel gas sensors with higher sensitivity and selectivity.     

电场对Ni3（dpa）4Cl2金属串配合物结构影响的理论研究

应用密度泛函UBP86方法对具有分子导线潜在应用性的金属串配合物Ni3(dpa)4Cl2进行研究,分析了外电场对配合物的几何构型和电子结构的影响.结果表明,零电场条件下存在沿着Ni63+轴及轴向配体Cl的Ni—Ni及Ni—Cl离域作用.沿金属轴Cl4→Cl5方向施加外电场,可使高电势端的Ni2—Cl4键长增大而Ni1—Ni2键长减小,低电势端的Ni3—Cl5键长减小而Ni1—Ni3键长增大;分子能量降低,偶极矩线性增大;HOMO与LUMO能隙减小,前线占据轨道分布向低电势方向移动且轨道能升高,空轨道分布则向高电势方向移动且轨道能降低,其中沿着金属轴方向离域的前线轨道分布及其轨道能随电场的变化尤为显著.在电场作用下,电荷分布发生改变,低电势端Cl5的负电荷向高电势端Cl4转移,但金属和桥联配体的电荷变化很小;同样,在电场作用下,配合物存在明显的结构变化和电子转移现象,呈现出类似导电过程中电子定向转移的变化规律.     

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.     

基于一氧化碳、二氧化碳和氧气分子吸附为探针的碳化钼、碳化钨、氮化钼和氮化钨的表面化学性质：密度泛函理论分析

作为具有吸引力的电极材料,过渡金属碳化物与氮化物被应用在许多电化学储能及能量转换领域. 本工作中,通过密度泛函理论计算,以及一氧化碳 （CO）, 二氧化碳（CO₂）和 氧气（O₂）分子的吸附来表征钼和钨的碳化物及氮化物,如碳化钼（Mo₂C）、碳化钨（W₂C）、氮化钼（Mo₂N）和氮化钨（Mo₂C）的表面化学性质. 这些探针分子可为研究钼和钨的碳化物及氮化物表面在酸性/碱性的氧化还原性质提供衡量方法. 计算结果表明,CO₂分子的吸附发生在路易斯碱位,其碱性降低顺序为α-W₂C(001) > α-W₂N(001) > β-Mo₂C(001) > γ-Mo₂N(100). 此外,CO和O₂分子吸附可用于评估上述碳化物及氮化物的还原能力,其还原性减小顺序为β-W₂C(100) > α-Mo₂C(100) > α-W₂N(001) > α-W₂C(001) > β-Mo₂C(001) > γ-Mo₂N(100). 由于还原本性,使得上述这些碳化物和氮化物成为在各种催化反应中有可能取代贵金属的良好候选材料.     

Rational design of FLP catalysts for reversible H2 activation: A DFT study of the geometric and electronic effects

The thermodynamics of reversible H₂ activation could be controlled by adjusting substituents of LA group and using different polar solvents, which forges a guide to design potential FLPs catalysts for reversible H₂ activation.     

脂肪胺水溶液吸收CO2的热力学参数的密度泛函理论研究

采用密度泛函理论研究CO2在脂肪胺水溶液热力学参数．研究的脂肪胺包括烷基胺、链烷醇胺、二胺以及氨基酰胺．在B3LYP/6-311＋ G（d,p）水平计算脂肪胺在CO2气相中的振动频率．通过连续介质模型在HF/6-31G（d）水平计算了溶剂几何优化的标准自由能,评价了CO2吸收到脂肪胺水溶液过程有关的两个重要参数：酸解离常数和标准焓变二者之间大致呈线性关系．随着胺碱度的提高,CO2吸收过程释放的热量增加,则胺再生所需的能量增加．     

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.     

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.     

A DFT study on mechanisms of CO2 coupling with propargylic alcohols using alkali carbonates

The mechanisms of CO₂ coupling with the propargylic alcohol using alkali carbonates M₂CO₃ (M = Li, Na, K, Cs) have been investigated by means of density functional theory calculations. The calculations reveal that the target product tetronic acid (TA) is yielded through two stages: (a) the formation of the α-alkylidene cyclic carbonate (αACC) intermediate via Cs₂CO₃-mediated carboxylative cyclization of the propargylic alcohol with CO₂, and (b) the conversion of the αACC intermediate with Cs₂CO₃ to produce the cesium salt of the TA. Since the overall kinetic barriers for the two stages are comparable and affordable, the excellent chemoselectivity to the TA should be primarily originated from the high thermodynamic stability of the cesium salt of the TA. Moreover, relative to the TA, the possibility to yield the by-product acyclic carbonate can be excluded due to the both kinetics and thermodynamic inferiority. This result is different from the organic base-mediated reaction. Alternatively, our calculations predict that CsHCO₃ together generated with the cesium salt of the TA might also be an available mediating reagent for the incorporation of CO₂ with the propargylic alcohol. Compared to other alkali carbonates M₂CO₃ (M = Li, Na, K), the stronger basicity of Cs₂CO₃ and the lower ionic potential of cesium ion can raise the effective concentration of the αACC intermediate, and thus the conversion of the αACC intermediate into the cesium salt of the TA can be achieved with high yield.     

理论计算研究二维/二维BP/g-C3N4异质结的光催化CO2还原性能

Photocatalytic reduction of CO₂ to hydrocarbon compounds is a promising method for addressing energy shortages and environmental pollution. Considerable efforts have been devoted to exploring valid strategies to enhance photocatalytic efficiency. Among various modification methods, the hybridization of different photocatalysts is effective for addressing the shortcomings of a single photocatalyst and enhancing its CO₂ reduction performance. In addition, metal-free materials such as g-C₃N₄ and black phosphorus (BP) are attractive because of their unique structures and electronic properties. Many experimental results have verified the superior photocatalytic activity of a BP/g-C₃N₄ composite. However, theoretical understanding of the intrinsic mechanism of the activity enhancement is still lacking. Herein, the geometric structures, optical absorption, electronic properties, and CO₂ reduction reaction processes of 2D/2D BP/g-C₃N₄ composite models are investigated using density functional theory calculations. The composite model consists of a monolayer of BP and a tri-s-triazine-based monolayer of g-C₃N₄. Based on the calculated work function, it is inferred that electrons transfer from g-C₃N₄ to BP owing to the higher Fermi level of g-C₃N₄ compared with that of BP. Furthermore, the charge density difference suggests the formation of a built-in electric field at the interface, which is conducive to the separation of photogenerated electron-hole pairs. The optical absorption coefficient demonstrates that the light absorption of the composite is significantly higher than that of its single-component counterpart. Integrated analysis of the band edge potential and interfacial electronic interaction indicates that the migration of photogenerated charge carriers in the BP/g-C₃N₄ hybrid follows the S-scheme photocatalytic mechanism. Under visible-light irradiation, the photogenerated electrons on BP recombine with the photogenerated holes on g-C₃N₄, leaving photogenerated electrons and holes in the conduction band of g-C₃N₄ and the valence band of BP, respectively. Compared with pristine g-C₃N₄, this S-scheme heterojunction allows efficient separation of photogenerated charge carriers while effectively preserving strong redox abilities. Additionally, the possible reaction path for CO₂ reduction on g-C₃N₄ and BP/g-C₃N₄ is discussed by computing the free energy of each step. It was found that CO₂ reduction on the composite occurs most readily on the g-C₃N₄ side. The reaction path on the composite is different from that on g-C₃N₄. The heterojunction reduces the maximum energy barrier for CO₂ reduction from 1.48 to 1.22 eV, following the optimal reaction path. Consequently, the BP/g-C₃N₄ heterojunction is theoretically proven to be an excellent CO₂ reduction photocatalyst. This work is helpful for understanding the effect of BP modification on the photocatalytic activity of g-C₃N₄. It also provides a theoretical basis for the design of other high-performance CO₂ reduction photocatalysts.      

金属串配合物(n,m)[Cr3(PhPyF)4Cl2](n=2, 3, 4; m=2, 1, 0)的配位结构及其与电场的关系

应用密度泛函理论BP86 方法研究具有分子导线潜在应用的金属串配合物(n, m)[Cr₃(PhPyF)₄Cl₂](HPhPyF=N, N'-苯基吡啶基甲脒; n=2, 3, 4; m=2, 1, 0)的配位结构及其受电场作用的影响, n、m分别表示PhPyF-的苯环在左侧和在右侧的配体个数. 结果表明: (1) 零电场下, 四个PhPyF-的(2, 2)、(3, 1)和(4, 0)三种配位方式能量差别很小, 为竞争态, (2, 2)最稳定. (4, 0)结构中两端轴向配体Cl 均可与Cr 配位, 且Cl₄―Cr1 键比Cl5―Cr3键更强, 若作为分子器件可与电极结合, 这与(4, 0)[CuCuM(npa)₄Cl][PF₆](M=Pd, Pt; Hnpa=2-萘啶苯胺)靠近苯环一端的轴向配体无法与M配位不同. (2) 在(2, 2)、(3, 1)和(4, 0)中, Cr₃⁶⁺链均具有三中心三电子离域σ键, 但离域性逐渐减弱. 随四个PhPyF-配位方式趋于一致, 分子极性逐渐增大, 由Cl₄指向Cl5(Z)方向, Cr1的α自旋密度增大, Cr2 的β和Cr3 的α自旋密度减小. (3) 分子的几何结构和电子结构在电场下发生规律性变化, 在-Z方向电场作用下, (3, 1)、(4, 0)电子移动方向与极性方向相同, 使分子的键长、自旋密度、电荷和能隙变化显著性均大于Z方向电场, 且极性越大变化越显著, 有利于提高分子导电性.     

外电场对N@C60, P@C60, As@C60分子结构和性质的影响

用量子力学方法研究了N@C60, P@C60, As@C60分子的几何和电子特征. 计算结果表明, 形成富勒烯包合物后, 碳笼只有微小的变形, 3种内包原子在笼中处于不同的位置, 碳笼与内包原子之间有明显的电荷转移和自旋轨道相互作用, 生成能分别为6.32, 70.88, -53.05 kJ/mol. 内包原子的3个单占据分子轨道(SOMO)能量变化很大, 并由于和碳笼作用而发生劈裂. 在外电场作用下, 分子的电子密度沿电场方向发生转移.分子的能量随外加电场的增强而降低. 分子轨道能级、能隙及SOMO轨道的能量和能级劈裂也发生了变化.     

A DFT analysis of the vibrational spectra of nitrobenzene

Raman and FTIR, spectra of nitrobenzene, nb, and its isotopomers, nb-¹⁵N, nb-¹³C₆ and nb-d₅, were obtained and the fundamental vibrational modes assigned with the aid of a B3LYP/6-311+G** calculation, without the need for scaling of the force constants. The changes in vibrational coupling between the nitro and benzene groups upon certain isotopic substitutions are well modelled by the calculation, which is able to reproduce the isotopic shifts in frequencies for the nitro vibrations, as well as changes in IR intensities.     

A combined electrochemical and DFT study of the lattice strain effect on the surface reactivity of Pd

We report a combined study of electrochemical experiments and ab initio calculations on tuning the surface reactivity of Pd via a compressive lattice strain achieved by employing nanoparticles of Pd-Cu alloys with a Pd-rich surface.Surface oxygen-containing species were used as the probing molecule for revealing the surface reactivity.Both density functional theory (DFT) calculations and experiments showed linear relationships,with very close slopes,between the adsorption strength of OH_(ads) and the Pd lattice constant.Not only is this work a successful realization of controllable modulation in the surface reactivity,but it also provides valuable information for the rational design of Pd-based catalysts for fuel cell applications.     

A DFT variational approach to Hooke''s atom based on local-scaling transformations

The local-scaling transformation version of density functional theory, LS-DFT, is employed in order to construct energy functionals for Hooke's atom. The components of the energy are analyzed and the resulting exchange and correlation potentials are compared with the exact ones. In addition, the representation of the exact one-particle density in terms of the various components of the total energy density is discussed.     

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.