DFT investigation of endohedral boron oxide nanocapsules: Encapsulation of He, Ne, Ar, H, N, and Cl atoms

The electronic structure and stabilization energy of spherical and pyramidal shapes of boron oxide nanocapsules (X@B₂₀O₃₀, X = He, Ne, Ar, H, N, Cl) were investigated by long-range and dispersion corrected density functional theory (DFT + Disp) including CAM-B3LYP, B3LYP-D3, ωB97X-D and B2PLYP-D methods. Based on these calculations, the formation of nanocapsules is an exothermic process (except for Cl@B₂₀O₃₀). The spherical boron oxide nanocapsules are mainly stabilized by dispersion, while the stability of pyramidal complexes is mainly due to monomer relaxation energy. The theoretical results obtained in this work show that the boron oxide capsule is a good potential candidate for gas storage.     

Conformational behavior of simple furanosides studied by optical rotation

Experimental and theoretical specific optical rotations (OR) of anhydro, epithio, and epiminoderivatives of methyl tetrofuranosides in chloroform solutions have been compared and used as a tool for exploring their conformational behavior. The potential energy surfaces of these saccharides with reduced flexibility were examined with the density functional theory and the MP2 and CCSD(T) wavefunctions methods. Theoretical ORs were obtained by Boltzmann averaging of values calculated for local minima. Resultant rotations could be used to assess the quality of the DFT and MP2 relative conformer energies. OR values calculated for equilibrium geometries in vacuum were significantly improved when the solvent was accounted for by a polarizable continuum model and first and diagonal second OR derivatives were used for an anharmonic vibrational averaging. The DFT used as a default method reproduced the experimental data fairly well. A modified B3LYP functional containing 70% of HF exchange further improved the results. Because of the strong dependence of OR on the conformation, not only the absolute configuration could be determined, but also the conformational populations were estimated. Likewise, the predicted dependence of OR on the light wavelength well agreed with experiment. The increasing precision of the contemporary computational methods thus makes it possible to relate the specific rotation to more detailed features in molecular structure. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

一系列新型硼氮化合物的理论研究

借助密度泛函理论,在B3LYP/6-311 G**和BP86/6-311 G**水平上,对一系列包含BNN单元的硼氮化合物BNN,H3BNN,NNBH2-BH2NN,(BNN)2H2,NN-BBNN,(BNN)3 ,(BNN)42 ,(BNN)5-,(BNN)6,(BNN)7 和(BNN)82 进行了理论计算研究.结果表明:在这些硼氮化合物中,尤其是BNN,B原子和N2配体之间存在着σ-π反馈作用.这种作用增强了B-N键,而活化了N-N键.结果还显示,(BNN)3 ,(BNN)42 ,(BNN)5-,(BNN)6,(BNN)7 和(BNN)82 都是具有平面单环结构并且满足4n 2规则的芳香性体系.     

Au10团簇结构与电性质的理论研究

使用4种流行的泛函(BPW91, B3PW91, PW91和B3LYP)考查了若干Au10团簇结构的稳定结构, 获得了能量最有利的6种异构体(其中2种以前未见报道), 并在此基础上进一步用MP2方法校准了它们的相对稳定性, 分析了它们的电子性质以及最稳定异构体与氧分子的化学反应性能. 计算结果表明Au10团簇异构体的相对稳定性明显依赖所使用的理论方法和泛函, 密度泛函结果显示Au10倾向于采用平面结构, 且不同的泛函给出异构体的相对稳定性次序也不相同, 而MP2计算则显示三维空间结构的Au10团簇更稳定, Au10可能是金团簇从二维结构到三维结构演化的一个临界点.     

Complexes of C60 fullerene with simple donor molecules: Theoretical study

The complex formation between fullerene C60 and simple donor molecules such as dimethyl ether, dimethylamine, dimethylsulfide, furan, pyrrole, and thiophene has been studied applying the hybrid MP2/6‐31G(d′):PM3 ONIOM approach for geometry optimization. Local implementation of Møller–Plesset perturbation theory in combination with 6‐31G(d) and 6‐311G(d,p) basis sets was used for binding energies estimation of fullerene complexes. Two factors were found to contribute most to the complex stability: the polarizability and molecular volume of donor molecule. As follows from positive stabilization energies at the Hartree–Fock level, the stabilization of fullerene complexes is entirely due to dispersion interactions in accordance with available experimental data. The calculations show that for donors of similar molecular volume the binding energy of molecular complex increases with polarizability of donor molecules. Similarly, for such complexes the partial charges on molecules increase with decreasing of ionization potentials of donor molecules. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

A DFT study on the healing of N‐vacancy defects in boron nitride nanosheets and nanotubes by a methylene molecule

In the present work, density functional theory calculations are used to investigate the healing mechanism of a N‐vacancy defect in boron nitride nanosheet (BNNS) or nanotube (BNNT) with a CH₂ molecule. The healing process starts with the chemisorption of CH₂ at the defect site, followed by its dehydrogenation over the surface. Next, a H₂ molecule is produced which can be easily released from the surface due to its small adsorption energy. For the dehydrogenation of CH₂ molecule over the defective BNNS or BNNT, the first C? H bond dissociation is the rate determining step. Our results indicate that the dehydrogenation of CH₂ over BNNS is both thermodynamically and kinetically more favorable than over BNNT. Besides, this study proposes a novel method for achieving C‐doped BNNSs and BNNTs. Given that the healing process proceeds without using a metal catalyst, therefore, no any purification is needed to remove the catalyst.     

Adsorption of nitrous oxide on the(6,0) magnesium oxide nanotube

Nitrous oxide adsorption on the pristine（6,0） magnesium oxide nanotube was studied by using density functional theory calculations.We present the nature of the N₂O interaction in selected sites of the nanotube.Adsorption energies corresponding to adsorption of the N₂O on the nanotube were calculated to be in the range -11.67 to -22.21 kJ mol^-1.Our results indicate that the N₂O molecule has a weak physical adsorption on the pristine models due to weak Van der Waals interaction between the nanotubes and N₂O molecule.The important results can be useful in production of the N₂O sensors.     

A quantum chemistry study: a new kind of boron nitrides

At the B3LYP/6-311+G** and the BP86/6-311+G** levels of theory, BNN, H(3)BNN, NNBH(2)-BH(2)NN, (BNN)(2)H(2), NNBBNN, (BNN)(3) (+), (BNN)(4), (BNN)(4) (2+), (BNN)(4) (2-), B(4)(NN)(2), (BNN)(5) (-), (BNN)(6), (BNN)(7) (+), and (BNN)(8) (2+) are investigated. Neutral (BNN)(4) is aromatic with its triplet state but antiaromatic with its singlet state. (BNN)(4) dication favors D(2d) structure, while (BNN)(4) dianion favors a planar D(4h) structure. (BNN)(3) (+), (BNN)(4) (2-), (BNN)(5) (-), (BNN)(6), (BNN)(7) (+), (BNN)(7) (3-), (BNN)(8) (2+), and (BNN)(8) (2-) are all aromatic with planar monocyclic conformation, following the 4n + 2 rule. Moreover, according to the CASSCF and MRCI calculations, the planar B(4)(NN)(2) of D(2h) symmetry prefers to be a sigma-pi diradical in spite of open-shell singlet or triplet and is also aromatic. Akin to the sigma-pi back interaction in compounds containing transition metal, there exists the sigma-pi back interaction between boron and N(2) ligand among some species reported herein, which strengthens B(-)N bond but activates N-N bond, especially in (4)Sigma(-) BNN. The T-shaped structure lies lowest in energy among seven isomers of the (BNN)(2)H(2) dimer, and the parallel-displaced structure is favored between two isomers of the (BNN)(6) dimer.     

Pathways of cycloaddition of carbodiimides to N-alkenylidenetriflamides: A theoretical study

Possible cyclization pathways for the reaction of (1E,2E)-N-(but-2-en-1-ylidene)triflamide with N,N'-dimethylcarbodiimide have been investigated by DFT and MP2 calculations. The [4+2] route is shown to be thermodynamically unfavorable due to a small content of the reactive s-cis conformer of the azadiene. The [2_CN+2_CN] route has ΔGº>0 and therefore is thermodynamically forbidden. The only allowed route is the [2_CN+2_CC] cycloaddition, which has ΔGº < 0 and leads to 2-methylimino-3-(2-trifliminomethyl)-1,4-dimethylazetidine with further isomerization to 3-(triflamidomethylidene)-2-methylimino-1,4-dimethylazetidine in full agreement with the experimental results. These results indicate the necessity of considering free energy changes rather than only enthalpy changes for accurate prediction of the course of cyclization reactions.     

AlCl3催化歧化制备二甲基二氯硅烷的DFT和MP2研究(II)

研究一甲基三氯硅烷与三甲基氯硅烷分别与三氯化铝作用并得到中间体后, 中间体分别与一甲基三氯硅烷和三甲基氯硅烷作用的机理, 反应的IRC (Intrinsic reaction coordinate)曲线, 各关键原子沿IRC的变化曲线及产物的理论产率. 结果发现, 中间体趋于与一甲基三氯硅烷作用生成二甲基二氯硅烷, 且三甲基氯硅烷的转化率高于一甲基三氯硅烷. 实验结果与计算结果吻合.     

AlCl_3催化歧化制备二甲基二氯硅烷的DFT和MP2研究(II)

研究一甲基三氯硅烷与三甲基氯硅烷分别与三氯化铝作用并得到中间体后,中间体分别与一甲基三氯硅烷和三甲基氯硅烷作用的机理,反应的IRC(Intrinsicreactioncoordinate)曲线,各关键原子沿IRC的变化曲线及产物的理论产率.结果发现,中间体趋于与一甲基三氯硅烷作用生成二甲基二氯硅烷,且三甲基氯硅烷的转化率高于一甲基三氯硅烷.实验结果与计算结果吻合.     

钙硼对CuO/Al_2O_3催化剂结构及醋酸仲丁酯氢解性能的影响

以经氧化钙和氧化硼改性的氧化铝为载体,采用浸渍法制备了负载型CuO/Al2O3催化剂,采用XRD、BET、TPR和NH3-TPD技术对催化剂CuO/Al2O3进行了表征.结果表明,氧化硼既可以作为结构性助剂提高铜在催化剂表面的分散度,又可以作为电子性助剂有利于催化剂表面氧化铜物种的稳定;氧化钙的引入降低了催化剂表面酸性,有利于催化剂的选择性提高.采用氧化硼和氧化钙改性的Cu10B20Ca30为催化剂,醋酸仲丁酯转化率可达99.5%,生成仲丁醇和乙醇的选择性分别达98.9%和97.8%.     

Molecule‐adapted basis sets optimized with a quantum Monte Carlo method

The Monte Carlo simulated annealing method is adapted to optimize correlated Gaussian‐type functions in nonrelativistic molecular environments. Starting from an atom‐centered atomic Gaussian basis set, the uncontracted functions are reoptimized in the molecular environments corresponding to the H₂O, CN^?, N₂, CO, BF, NO⁺, CO₂, and CS systems. These new molecular adapted basis sets are used to calculate total energies, harmonic vibrational frequencies, and equilibrium geometries at a correlated level of theory. The present methodology is a simple and effective way to improve molecular correlated wave functions, without the need to enlarge the molecular basis set. Additionally, this methodology can be used to generate hierarchical sequences of molecular basis sets with increasing size, which are relevant to establish complete basis set limits. © 2014 Wiley Periodicals, Inc.     

Density functional theory studies of effects of boron replacement on the structure and property of RDX and HMX

In this study, based on two model nitramine compounds hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5, 7-tetrazocine (HMX), two series of new energetic molecules were designed by replacing carbon atoms in the ring with different amounts of boron atoms, their structures and performances were investigated theoretically by the density functional theory method. The results showed that the boron replacement could affect the molecular shape and electronic structure of RDX and HMX greatly, and then would do harm to the main performance like the heat of formation, density, and sensitivity. However, the compound RDX-B2 is an exception; it was formed by replacing two boron atoms into the system of RDX and has the symmetric boat-like structure. Its oxygen balance (4.9%), density (1.91 g/cm³), detonation velocity (8.85 km/s), and detonation pressure (36.9 GPa) are all higher than RDX. Furthermore, RDX-B2 has shorter and stronger N NO₂ bonds than RDX, making it possesses lower sensitivity (45 cm) and better thermal stability (the bond dissociation energy for the N NO₂ bond is 204.7 kJ/mol) than RDX. Besides, RDX-B1 and HMX-B4 also have good overall performance; these three new molecules may be regarded as a new potential candidate for high energy density compounds.     

Theoretical study on the adduct of chlorine trifluoride oxide and boron trifluoride—molecular and crystal structures,vibrational spectrum,and thermodynamic properties

To search for the most stable form and understand the relationship between the structure and property of the adduct of chlorine trifluoride oxide and boron trifluoride, various isomeric structures were constructed and optimized with the first principle methods. The most stable structure of the adduct has an ionic form. The vibrational spectra were calculated and assigned, and used to compute the standard thermodynamic properties. Molecular mechanics method was employed to predict the possible crystal packing of the adduct, and density functional theory method was used to refine the crystal structure and to calculate the energy band. The obtained band gap (3.40 eV) shows that the crystal is insensitive and stable under closed environment as was found experimentally. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

A computational study of the cooperativity in clusters of interhalogen derivatives

The clusters, up to four monomers, of the interhalogen derivatives (FCl, FBr, and ClBr) have been studied by means of ab initio and DFT methods, up to MP2/aug-cc-pVTZ computational methods. Two dispositions, linear and cyclic, of the clusters have been studied. Cooperative effects in the geometry, energy, and electron density have been observed in the linear and cyclic dispositions of these clusters. The Natural Energy Decomposition Analysis shows that the main source of the interaction corresponds to the polarization term. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Gas storage in nanoporous materials

Gas storage in solids is becoming an ever more important technology, with applications and potential applications ranging from energy and the environment all the way to biology and medicine. Very highly porous materials, such as zeolites, carbon materials, polymers, and metal-organic frameworks, offer a wide variety of chemical composition and structural architectures that are suitable for the adsorption and storage of many different gases, including hydrogen, methane, nitric oxide, and carbon dioxide. However, the challenges associated with designing materials to have sufficient adsorption capacity, controllable delivery rates, suitable lifetimes, and recharging characteristics are not trivial in many instances. The different chemistry associated with the various gases of interest makes it necessary to carefully match the properties of the porous material to the required application.     

六甲基二硅烷催化裂解的理论计算

采用密度泛函(DFT)及二级微扰理论(MP2)对六甲基二硅烷的催化裂解过程进行了计算.结果显示,该反应分三步进行,各步的能垒分别为144.9、77.4及214.9 kJ·mol-1,决定反应速度的是第三步.总反应是放热的,其中各步的焓变分别为22.4、-237.6、-127.6 kJ·Mol-1,反应的标准吉布斯自由能变为-348.7 kJ·mol-1,平衡常数为1.221×1061,在常温及常压下有较大的裂解倾向,理论产率比较高,计算结果与实验结果一致.