A systematic investigation on the aromaticity and kinetic stability of fullerene C40 isomers

The aromatic character of fullerene C₄₀ isomers was examined by the topological resonance energy and the percentage topological resonance energy models. It was found that they all are highly aromatized at the polyvalent anionic states. The nucleus‐independent chemical shifts at the cage center and the 2(N + 1)² rule cannot be used as an indicator of the aromatic stabilization for C₄₀ isomers and their molecular ions. In addition, we utilized the bond resonance energy model to estimate the kinetic stability of C₄₀ isomers and their molecular ions. The results reveal that the kinetic stability of C₄₀ isomers can be greatly enhanced at their polyvalent anionic states. Both the aromaticity and kinetic stability are closely related to the local structure and the cyclic motion of π electrons. Copyright © 2011 John Wiley & Sons, Ltd.     

First-principle study of geometries, electronic structures and vibrational spectra of neutral and anionic onion-like [As@Ni12@As20］

We present results of first-principle study for both neutral and anionic onion-like [As@Ni₁₂@As₂₀］. The ground-states of singly-charged and doubly-charged anions deviate from ideal I_h symmetrical geometry because of Jahn--Teller effect, whereas the triply-charged singlet and neutral quartet have similar stable geometries of I_h symmetry. The infrared and Raman spectra may provide a way to determine various charge states of this molecule with the same symmetry. Based on our systematical calculations, we suggest additional experimental measurements in order to determine the appropriate functional with great confidence, which should be important in the research for future quantum dot devices.     

Molecular properties of selenomaltols: new interesting ligands for bioactive metal complexes

Properties of numerous selenium derivatives of maltol (3‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one), which is an important ligand in medicinal chemistry, were studied. Selenium derivatives were obtained using consecutive in silico replacements of maltol oxygen atoms, which produced three mono‐substituted, three di‐substituted and one tri‐substituted derivatives. The geometry optimisations for these compounds in neutral, anionic and cationic forms were performed at the B1LYP/6‐311++G** level of theory. The aromatic properties of the considered selenium compounds were studied in their heterocyclic rings using several indices of aromaticity: harmonic oscillator model of aromaticity, nucleus independent chemical shift(0), nucleus independent chemical shift(1), aromatic stabilisation energy, H index, para delocalisation index and multicentre index. The methods cover all of the main types of aromaticity indices: geometric, magnetic, energetic and electronic. The calculated data show the identical aromaticity order (cation > neutral molecule > anion) for maltol and its thio and seleno derivatives. The predicted aromaticity levels of selenomaltols were compared with the previously studied maltol and various thiomaltols. Copyright © 2015 John Wiley & Sons, Ltd.     

C20分子异构体的电子态

使用量子化学从头计算方法优化了C₂₀分子三种异构体（环形、碗形和笼形）的单重和三重电子态几何结构。从优化的几何结构出发，由二阶微扰（MP2）方法得到的单点能给出了一个不符合Hund法则的结果，也就是三种异构体的能量都是单重电子态的最低。使用UHF波函数给出了三种异构体的总电荷密度和静电势，结果显示在笼形和碗形结构的中心区域存在负电荷。最后，本文分析了环形结构的成键特征。     

异质富勒烯C76BN的UV和IR光谱研究

用INDO方法对C76BN的22种可能异构体进行较系统的理论研究,表明最稳定的两种异构体52,53-C76BN和29,28-C76BN是B和N直接相连并位于C78(C2v)椭球长轴附近的6／6键上;用INDO／SCI方法计算C76BN的电子光谱表明,其长波吸收峰与C78(C2v)相比发生红移．用AM1方法对C76BN的四种稳定异构体进行构型优化及红外光谱研究表明,BN单元的取代削弱C原子之间的共轭而使红外频率变小．     

Theoretical study of the [Si,C, P,O] potential energy surface

The structures, energetics, spectroscopies and stability of the doublet [Si, C, P, O] radical are explored at the density functional theory and ab initio levels. Eighteen isomers connected by 22 interconversion transition states are located at the DFT/B3LYP/6-311G(d) level. The structures of the kinetically stable isomers and the relevant transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311 + G(2df) single-point energy calculations. At the QCISD/6-311G(d) level, the lowest-lying isomer is the cyclic O-cCSiP 8 (0.0 kcal/mol) with considerable kinetic stability of 22.0 kcal/mol. In addition, two bent isomers OSiCP 1 (7.3 kcal/mol) and SiCPO 3 (34.7 kcal/mol) also possess considerable kinetic stability (more than 10.0 kcal/mol). As a result, three isomers 1, 3 and 8 are predicted to be possible candidates for future experimental and astrophysical detection. The bonding nature of the three isomers is analysed. The calculated results are compared with those of the analogous radical [Si, C, N, O]. Implications in the laboratory and interstellar space are also discussed. The predicted structures and spectroscopic properties are expected to be informative for the identification of [Si, C, P, O] in the laboratory and space.     

Theoretical studies on aromaticity of selected hydroxypyrones and their cations and anions. Part 2. Electron delocalisation in the OCCO group

Electron delocalisation in the OCCO part of hydroxypyrones with two exocyclic oxygens linked by two carbon atoms was studied using well‐known aromaticity indices like: HOMA, EN, GEO, NICS(0) and NICS(1). This part of hydroxypyrones is very important due to the fact that the two exocyclic oxygens of deprotonated hydroxypyrone units are responsible for metal ion binding. Values of the aromaticity indices were obtained for geometries calculated by several theoretical methods (HF, SVWN, B3LYP and B1LYP) with 6‐311 ++ G(d,p) basis set. Electron delocalisation in the corresponding cations and anions was also considered. The data obtained in this work revealed that the relative delocalisation order in the OCCO group is the same as the aromaticity order determined earlier for the heterocyclic rings of hydroxypyrones (anions < neutral molecule < cation). The problem of quasiaromaticity in neutral hydroxypyrones and their cations is also considered and discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Theoretical studies on aromaticity of selected hydroxypyrones. Part 3#. Chelatoaromaticity phenomenon in metalcomplexes of hydroxypyrones

The aim of this project is to study the aromatic properties of various forms (neutral, cationic, and anionic) of selected hydroxypyrones (pyromeconic acid, maltol, and ethylmaltol) and their metalcomplexes with aluminum, gallium, and indium ions. Aromaticity of hydroxypyrone metalcomplexes is important because it can influence the stability of such complexes, which is crucial for their applications in medicinal and environmental chemistry. Results from ten different indices of aromaticity (HOMA, NICS(0), NICS(1), NICS_scan, ASE_iso, PDI, FLU, I_ring, MCI, and KMCI) show that aromaticity in hydroxypyrones decreases in the order cations > neutral molecules > anions. Performed calculations situate the aromaticities of ligands in metalcomplexes close to their respective cations. This means that complexation causes a significant increase of the aromaticity of ligands, which stabilizes formed chelatocomplexes. On the other hand, we clearly show that rings that are involved in binding metal ions are not aromatic. Copyright © 2010 John Wiley & Sons, Ltd.     

Structure prediction and aromaticity of acenes and phenylenes series. A combination method between asymmetric Kekulé structures

The combination method between asymmetric Kekulé structures (CMAK) was expanded to the structure prediction of a series of acenes and phenylenes. The structures predicted by the CMAK correspond to those calculated by the ab initio molecular orbital (MO) and B3LYP density functional methods. The CMAK can characterize the structures. The aromaticity for the whole ring and each ring in the treated compounds was estimated by the index of deviation from aromaticity (IDA). The estimated aromaticity corresponds fairly well to the characterization of the structure predicted by the CMAK. The predicted structures of linear acenes reveal the aromaticity of the central ring and also explain its reactivity. The side ring in [n]phenacene shows high aromaticity. The critical difference in the structure and aromaticity for the central six‐membered ring of the isomers benzo[1,2:4,5]dicyclobutene and benzo[1,2:5,6]dicyclobutene was explained. Copyright © 2012 John Wiley & Sons, Ltd.     

Geometric and electronic structures of B12C6N6 fullerene

An electron deficient fullerene B₁₂C₆N₆ is studied by using ab initio calculations. The structure is generated by replacing N with C in the B₁₂N₁₂ cage to ensure only B–C and B–N bonds are formed. All the possible isomers are optimized and the low energy structures are determined. C and N atoms in the low energy isomers are inclined to segregate and form B₂C₂ and B₂N₂ squares. Natural bond analysis shows that the atomic orbitals of B, C and N in this cage hybrid approximately in sp^2.3 and then form B–C and B–N bonds. The 2p orbitals perpendicular to the cage surface are partially occupied and the molecular orbitals formed by these orbitals are highly delocalized. The natural charge on N is about −1.17 in both B₁₂N₁₂ and B₁₂C₆N₆, and the charge on C is −0.72 to −0.60. The molecular orbital compositions show that the B–N bonds are the same in B₁₂N₁₂ and B₁₂C₆N₆, and the B–C bonds possess stronger covalent character. The HOMO of B₁₂C₆N₆ is formed by 2p of B and C, and the LUMO is formed by 2p of C. The energy gap of C₂₄, B₁₂N₁₂ and B₁₂C₆N₆ is 2.52, 6.84 and 3.22 eV, respectively.     

碳硼富勒烯衍生物C18B2M(M=Li,Ti, Fe)的储氢性能计算研究

本文使用密度泛函理论(density functional theory, DFT)中的广义梯度近似(generalized gradient approximation, GGA)研究了经碱金属原子Li、过渡金属原子Ti和Fe原子修饰的富勒烯C₁₈B₂M(M=Li, Ti, Fe)的储氢性能. 研究发现, C₁₈B₂由于B的替代掺杂, 比C₂₀对金属原子具有更高的结合能. 由平均吸附能分析可知: C₁₈B₂Li对H₂的吸附能力较弱, C₁₈B₂Fe对H₂的吸附能力过强, 而C₁₈B₂Ti对H₂的平均吸附能介于0.45-0.59 eV 之间, 介于物理吸附和化学吸附之间 (0.2-0.6 eV), 因此可以实现常温下的可逆储氢. C₁₈B₂M(M=Li, Ti, Fe)能够吸附的H₂数目最多分别为4, 6和4. 由储氢机理分析可知: C₁₈B₂Li主要通过碱金属离子激发的静电场来吸附H₂, 而C₁₈B₂Ti和C₁₈B₂Fe主要通过金属原子与H₂之间的Kubas作用来吸附H₂. 由于C₁₈B₂Ti既有较大的储氢数目, 又可以实现可逆储氢, 因此有望开发成新型纳米储氢材料.     

应变和C掺杂对单层BN纳米片的电子结构和磁学性质的影响

利用基于密度泛函理论的第一性原理计算方法, 研究了应变和C原子掺杂对单层BN纳米片的电子结构和磁学性质的影响. 计算结果表明未掺杂的单层BN纳米片具有宽的直接带隙, 在压缩和拉伸应变的作用下, 带隙会分别增大和减小, 但应变对带隙的调制整体效果不太明显. 单个C原子掺入BN纳米片的态密度揭示体系呈现出半金属性(Half-metallicity), 磁矩主要源于C 2p态, 而B 2p和N 2p态在极化作用下也能提供部分磁矩. 两个C原子掺入BN纳米片时, 磁性基态会随着C原子的间距发生变化: 当两C原子为最近邻(nn)和次近邻(nnn)时, 反铁磁态为磁性基态; 而当两C原子为次次近邻(nnnn)时, 铁磁态为基态, 并且其态密度也显示出半金属性.     

在同位旋SU(2)不变耦合模型中研究 p pbar -> n nbar 核子反应的重整化无穷阶链图效应

本文采用描述中性及荷电 pion 介子（pion0,pion+,pion-）与核子-反核子强相互作用的同位旋SU(2)不变耦合模型,计算出在pion0 及 pion+, pion- 重整化链图传播下 p pbar -> n nbar 核子反应微分截面的“精确”解析结果;并且将此结果与在 pion0 及 pion+, pion- 树图传播下的微分截面作了对比分析,得到相应的辐射修正重要信息。本文完成的工作对进一步深入研究三种荷电状态 pion 介子与核子-反核子强相互作用的同位旋SU(2)不变耦合模型以及深入理论探讨质子-反质子对撞实验,都将提供某些理论研究的参考价值。     

Ih和D5h对称的三金属氮化物富勒烯Sc3N@C80的几何结构、电子结构和磁学特性

采用密度泛函理论（density functional theory, DFT）方法对具有Ih和D5h对称的三金属氮化物富勒烯Sc3 N＠C80的几何结构、电子结构及其磁学特性进行了计算研究。几何结构优化显示掺杂Sc3 N之后,C80的结构只是发生了细微的变化,仍然保持了Ih 和D5h对称性。能级图和局部态密度图表明Sc原子对能级的变化贡献最大,掺杂之后能隙增加,简并度下降,增强了两种异构体的稳定性。磁学特性分析指出掺杂之后,Sc3 N的磁性完全淬灭,两种异构体均没有磁矩,都不能作为磁性材料。     

在同位旋SU(2)不变耦合模型中研究 p pbar -> n nbar 核子反应的重整化无穷阶链图效应

本文采用描述中性及荷电 pion 介子（pion0,pion+,pion-）与核子-反核子强相互作用的同位旋SU(2)不变耦合模型,计算出在pion0 及 pion+, pion- 重整化链图传播下 p pbar -> n nbar 核子反应微分截面的“精确”解析结果;并且将此结果与在 pion0 及 pion+, pion- 树图传播下的微分截面作了对比分析,得到相应的辐射修正重要信息。本文完成的工作对进一步深入研究三种荷电状态 pion 介子与核子-反核子强相互作用的同位旋SU(2)不变耦合模型以及深入理论探讨质子-反质子对撞实验,都将提供某些理论研究的参考价值。     

Ih和D5h对称的三金属氮化物富勒烯Sc3N@C80的几何结构、电子结构和磁学特性

采用密度泛函理论（density functional theory, DFT）方法对具有Ih和D5h对称的三金属氮化物富勒烯Sc3N@C80的几何结构、电子结构及其磁学特性进行了计算研究.几何结构优化显示掺杂Sc3N之后,C80的结构只是发生了细微的变化,仍然保持了Ih和D5h对称性.能级图和局部态密度图表明Sc原子对能级的变化贡献最大,掺杂之后能隙增加,简并度下降,增强了两种异构体的稳定性.磁学特性分析指出掺杂之后,Sc3N的磁性完全淬灭,两种异构体均没有磁矩,都不能作为磁性材料.     

C36团簇生长动力学及自由能

在2300 K的气相条件下,采用经典分子动力学方法对C₃₆团簇的生长过程进行模拟,并计算生长过程中出现的势能最低的20个异构体的相对概率.计算结果表明:团簇系统在100 ns左右达到动态平衡,出现概率最大的异构体是_2d而不是势能最低的D_6h.对于某些势能和自由能均较高的碗状异构体,在生长过程中以一定概率出现,其出现概率甚至高于某些经典构型.     

对全金属La2-4团簇芳香性的从头算理论研究简

我们将芳香性扩展到全金属阴离子团簇La2-4.运用从头算方法(B3LYP/LANL2DZ,B3PW91/LANL2DZ and MP2/LANL2DZ)进行了结构优化.计算结果显示,阴离子团簇有两个同分异构体,一个是C2v结构,另一个是正方形D4h结构.进一步对能量的分析得出,D4h结构比C2v结构更稳定.对最稳定的D4h结构计算了核独立位移(NICS),结果显示正方形的La2-4环呈现强芳香性.详细的分子轨道(Mos)分析揭示正方形的La2-4环拥有四个独立的离域化成键系统,每一个系统拥有两个电子,分别满足4n+2芳香性电子计算规则,因此呈现四重芳香性.     

对全金属La42-团簇芳香性的从头算理论研究

我们将芳香性扩展到全金属阴离子团簇La42-.运用从头算方法(B3LYP/LANL2DZ, B3PW91/LANL2DZ and MP2/LANL2DZ)进行了结构优化.计算结果显示,阴离子团簇有两个同分异构体,一个是C2v结构,另一个是正方形D4h结构.进一步对能量的分析得出,D4h结构比C2v结构更稳定.对最稳定的D4h结构计算了核独立位移(NICS),结果显示正方形的La42-环呈现强芳香性.详细的分子轨道(Mos)分析揭示正方形的La42-环拥有四个独立的离域化成键系统,每一个系统拥有两个电子,分别满足4n + 2芳香性电子计算规则,因此呈现四重芳香性.     

60keV N2+轰击生成BN纳米结构

报道了N2+离子轰击BN固体样品过程中,弯折BN片纳米结构和笼状小BN分子的形成.高分辨透射电子显微分析表明,厚度小于13nm的BN片具有高度可弯折性,也观察到了一些直径为0.4—1.8nm,接近于B₁₂N₁₂, B₁₆ N₁₆和B₂₀₈N₂₀₈的8面体笼状物.基于束流-固体相互作用观点,讨论了这些BN纳米结构的形成原因.