Computational studies of effects of tubular lengths on the NMR properties of pristine and carbon decorated boron phosphide nanotubes

Density functional theory (DFT) calculations were performed to investigate the effects of tubular lengths on the nuclear magnetic resonance (NMR) properties of boron phosphide (BP) nanotubes. To this aim, the properties of pristine and carbon decorated (C-decorated) models of representative zigzag and armchair BP nanotubes were investigated. The results indicated that the atoms at the edges of nanotubes do not detect any significant changes. The NMR properties of boron atoms only detect slight changes but those of phosphorous atoms are more notable.     

Interaction of vitamins A,B1, C,B3 and D with zigzag and armchair boron nitride nanotubes: A DFT study

In this work, based on the density functional theory, the interaction of vitamins A, B1, C, B3 and D with (5, 5) armchair and (9, 0) zigzag single-walled boron nitride nanotubes (BNNTs) are studied. It is found that binding of vitamins A, B1, C, B3 and D with (9, 0) and (5, 5) BNNTs is thermodynamically favorable. Calculated solvation energies show that the solubility of functionalized (9, 0) BNNTs is higher than that of functionalized (5, 5) BNNT, and both dissolutions in water are spontaneous. The results showed that BNNTs can act as a suitable drug delivery vehicle for vitamins A, B1, C, B3 and D within biological systems. This study may provide a new insight into the development of the functionalized boron nitride nanotubes as drug delivery systems for virtual applications.     

The pristine and carbon,silicon or germanium-substituted (10, 0) BN nanotube: A computational DFT study of NMR parameters

The geometrical structure and nuclear magnetic resonance (NMR) parameters of the pristine as well as carbon, silicon and germanium-doped (10, 0) boron-nitride (BN) nanotubes have been studied using a DFT-B3LYP method for the first time. When either a Ge, C or Si atom is substituted for a single B or N in the BN nanotube, the dopant atom extends outward from the surface of the nanotube. Our results show that Ge extends more from the surface than C or Si. It was found that the NMR parameters are significantly changed for those B and N nuclei that bond directly to C, Si or a Ge dopant. The calculations were carried out using the Gaussian 03 software package.     

单壁AlAs(111)纳米管结构和电子性质的密度泛函理论研究

通过卷曲立方AlAs(111)单层片(sheets)构造了一系列(n,0)和(n,m)一维单壁纳米管。用周期性密度泛函理论(DFT)计算并比较了不同类型AlAs纳米管在几何结构、能量及电子性质等方面的差别。计算结果表明锯齿型和椅型纳米管应变能均为负值,并随着管径变大而逐渐变小。然而,它们的带隙相当不同:椅型纳米管为间接带隙,随着管径的增大而带隙减小;锯齿型纳米管为直接带隙,管径为1.87 nm时存在着一个极大带隙值(2.11 eV)。这种不同主要源于锯齿型纳米管铝原子间3p轨道的耦合贡献。     

Systematic studies on the computation of nuclear magnetic resonance shielding constants and chemical shifts: the density functional models

We present a systematic density functional investigation on the prediction of the 13C, 15N, 17O, and 19F NMR properties of 23 molecules with 21 density functionals. Extensive comparisons are made for both 13C magnetic shieldings and chemical shifts with respect to the gas phase experimental data and the best CCSD(T) results. We find that the OPBE and OPW91 exchange-correlation functionals perform significantly better than some popular functionals such as B3LYP and PBE1PBE, even surpassing, in many cases, the standard wavefunction-based method MP2. Further analysis has been performed to explore the individual role played by various exchange and correlation functionals. We find that the B88 and PBE exchange functionals have a too strong tendency of deshielding, leading to too deshielded magnetic shielding constants; whereas the OPTX exchange functional performs remarkably well. We claim that the main source of error arises from the exchange functional, but correlation functional also makes important contribution. We find that the correlation functionals may be grouped into two classes. class A, such as LYP and B98, leads to deshielded NMR values, deteriorating the overall performance; whereas class B, such as PW91 and PBE, generally increases the absolute shieldings, which complements the exchange functionals, leading to improved results in the calculation of NMR data.     

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.     

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 study of NMR chemical shielding in 5-coordinate phosphorus compounds (phosphoranes)

Calculations of the phosphorus NMR chemical shielding in 5-coordinate phosphorus compounds have been carried out using the gauge-including-atomic-orbital (GIAO) 6-311+G(nd,p) basis set at both scaled density functional theory (sDFT) and estimated infinite order Møller–Plesset (EMPI) approaches. Results are generally in accord with previous studies on 3-coordinate phosphorus compounds but fail badly for compounds containing multiple chlorine atoms and indicate a need for a relativistic treatment of these species. We observe that some compounds with reported experimental ³¹P NMR chemical shifts far downfield of the calculated values are in fact in the range known from experiment and calculation to be in that expected for phosphonium ions; the reported structures need to be reconsidered.     

Spectroscopic and inclusion properties of G-series chemical warfare agents and their simulants: a DFT study

A computational protocol to predict the infrared spectra of chemical warfare agents (CWAs) tabun (GA), sarin (GB), soman (GD) and cyclosarin (GF) has been developed. Sarin was used to benchmark the method through gas phase simulations. DFT calculations using the EDF2 functional and diffuse 6-311++G** basis set was found to give the closest match to experimental infrared spectra. Using the same functional the 6-31G (2df, 2p) basis set was found to be superior when hydrated sarin was modelled. GA, GB, GD and GF, together with 11 commonly used simulants, were modelled in the gas and hydrated states. Complexes of GB and a number of CWA mimics with α-cyclodextrin were modelled to give insight into their different modes of inclusion.     

B28N28笼的稳定性及笼中四元环间键联类型对笼稳定性的影响

采用密度泛函方法对四、六元环组成的所有可能的的23个笼状B28N28结构进行了理论计算和拓扑学特性研究, 用三个指标N4x4(x=0, 1, 2)来描述相邻四元环间的键联类型, 结果发现B28N28笼的相对能量随N4x4值的增大而增大, 且N404对稳定性的影响起主导作用. 这一简单的拓扑学标准可以给出所有四六结构B28N28异构体的大致能量顺序, 并从ISR结构中挑选出能量较低的结构, 因此有望用于挑选大尺寸氮化硼团簇的热力学稳定结构.     

Exploring the electronic and magnetic properties of zigzag and armchair BC2N nanotubes: a DFT study

A density functional study is performed to investigate the electronic and magnetic properties of zigzag and armchair BC₂N nanotubes based on the ¹³C, ¹⁵N, and ¹¹B NMR parameters and natural charge analysis. We considered three types of zigzag nanotubes, ZZ-1, ZZ-2, and ZZ-3 (n, 0) with n = 3, 4, and 5, as well as two types of armchair nanotubes: AC-1 and AC-2 (n, n) with n = 3 and 4. The obtained results indicate the divisions of the electrostatic environments around C nuclei into a few layers, consistent with the calculated natural charges on C atoms. A good correlation is seen between the layers of chemical shielding isotropy as well as anisotropy, σ _iso, and Δσ, and the five local structures around carbon atoms. Successive BN units lead to larger ¹⁵N σ _iso values (96.5–105.5 ppm) in comparison with the individual BN units (74.3–92.0 ppm in the ZZ-2(n, 0) and 47.4–61.7 ppm in the ZZ-3(n, 0)). Slight differences in the values of ¹¹B σ _iso clarify diminutive diversity in the electron densities of boron nuclei, while Δσ values indicate the more apparent range of changes.     

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.     

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.     

Influence of NO2 attachment on the nuclear magnetic shielding tensors of N and B nuclei in C30B15N15 heterofullerene: a DFT study

Adsorption of nitrogen dioxide in three different configurations on the exterior surface of C₃₀B₁₅N₁₅ is studied using density functional theory calculations. To this end, we optimized the structures of raw C₃₀B₁₅N₁₅ and nine NO₂–C₃₀B₁₅N₁₅ complexes at the B3LYP/6-31G^* level of theory and then calculated chemical shielding (CS) tensors at the GIAO-B3LYP/6-311G^** level for the optimized structures. The calculated chemical shielding isotropy (CSI), chemical shielding anisotropy (CSA), and orientation of CS tensors (Euler angles) reveal that the adsorption configurations (nitro, trans-nitrite, and cis-nitrite) have different effects on the electronic structure of C₃₀B₁₅N₁₅. Natural atomic charges based on natural population analysis (NPA) were used to justify the changes in CSI values after gas sorption.     

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.     

尺寸效应对SiO2纳米管化学屏蔽张量的影响

运用密度泛函理论,对截面为三元环的有限长SiO2纳米管进行了研究.核磁共振(NMR)的结果表明,随着纳米管层数的增加,29Si和17O原子的各向同性化学屏蔽张量σiso和各向异性化学屏蔽张量△σ由两端向中间振荡直至趋于稳定值.对长度大于一定数值的有限长纳米管,中间层上原子的σiso和△σ值可作为更长的或无限长SiO2纳米管的理论预测值,这些结果对如何选取合理的有限长纳米管模型来研究无限长结构具有一定的指导意义.     

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.     

一种天然产物Wangzaozin A的细胞毒活性

从总序香茶菜Isodon racemosa (Hemsl) Hara植物中分离得到一个对人类肿瘤细胞Bel-7402和HD-8910具有毒活性的对映-贝壳衫烷型二萜Wangzaozin A化合物(1). 应用密度泛函理论(DFT)B3LYP方法, 对该分子的几何构型进行优化, 结果表明用B3LYP/6-31G(d)优化的几何参数与它的X射线衍射结构参数基本一致. 在优化的几何构型基础上, 采用规范不变原子轨道(GIAO)法, 在B3LYP理论水平分别用6-31G(d), 6-31G(d,p), 6-31+G(d,p)和6-31++G(d,p)基组进行核磁共振(NMR)化学位移值计算, 预测的1H和13CNMR化学位移值与实验值吻合; 统计误差分析表明, 用B3LYP/6-31G(d)优化的分子构型接近实际的分子构型. 因此, DFT方法适用这一类型化合物的构型和NMR参数进行预测. 在几何优化的基础上, 在B3LYP/6-31G(d)水平上, 对Wangzaozin A分子的静电位(MEP)进行理论计算. MEP三维图表明, 在Wangzaozin A分子中α-亚甲基环戊酮的羰基和羟基附近出现富电子区域(负电位), 起着供电子作用, 与受体的正电子区域结合. 这些结果从理论上支持了α-亚甲基环戊酮结构是一种抗肿瘤活性中心的看法.     

Sensing and catalytic decomposition of hydrogen peroxide by silicon carbide nanotubes: A DFT study

In this study, by carrying out detailed density functional theory calculations, we investigate the adsorption and stepwise decomposition of hydrogen peroxide (H₂O₂) over (6,0) and (7,0) zigzag silicon carbide nanotubes (SiCNTs). The results indicate that the H₂O₂ can be adsorbed on the exterior surface of the SiCNTs with noticeable adsorption energies and charge transfers. To gain insight into the catalytic activity of the surface, the interaction between the H₂O₂ and SiCNT is analyzed by detailed electronic analysis such as adsorption energy, charge density difference and activation barrier. The decomposition of H₂O₂ into O₂ and H₂ species can be viewed as the kinetically preferred reaction pathway for dehydrogenation of hydrogen peroxide over SiCNTs. There is also a curvature effect on the dehydrogenation kinetics of hydrogen peroxide, that small diameter SiCNTs with large curvature would be beneficial for decomposition of H₂O₂. © 2015 Wiley Periodicals, Inc.