Substituent effect on structure,stability, and aromaticity of novel BnNmC20–(n+m) heterofullerenes

We are focusing our calculations on the structural stabilities and electronic properties of 26 novel B_nN_mC_20–(n+m) heterofullerenes, with n, m = 1 ? 5, at B3LYP/6‐311++G** and B3LYP/AUG‐cc‐pVTZ levels of theory. Vibrational frequency calculations on C₂₀ and its analogues show that except B₂N₂C₁₆ (1) and B₂N₂C₁₆ (2), all other heterofullerenes are true minima. The heats of atomization energies, binding energy, band gaps (ΔE_HOMO‐LUMO), aromaticity, nucleus‐independent chemical shifts, thermodynamic stability, kinetic stability against electronic excitation, binding energy as a stability criterion of different configurations, geometrical parameters, conformational structures, conductivity, charge transfer, and possibility for hydrogen storage of these heterofullerenes strongly depend on their number of heteroatoms, topology, filling patterns, and locations as well as “B‐site and N‐site attachments.” B₅N₅C₁₀ contains 5 alternating boron and nitrogen atoms in the equatorial position. It is predicted to be thermodynamically and kinetically the most stable against electron excites. Thus, it is energetically favorable and its electronic properties as well as stabilities make it perhaps a good candidate for an experimental investigation and testing verification.     

A comparative study on the Ge6C14 heterofullerene nanocages: a density functional survey

Ten C₁₄Ge₆ heterofullerene isomers of C₂₀ have been investigated by density functional theory (DFT) methods with Becke 3‐Parameter (Exchange), Lee, Yang and Parr (B3LYP) functional at the 6‐311 + G*, 6‐311++G** and AUG‐cc‐pVTZ levels. In contrast to identical bonds in the latter, contractions of C═C double bonds are encountered at the expense of longer C―Ge bonds in the former. Vibrational frequency analysis confirms that all of the nanocages are true minima. In contrast to the common belief, for obtaining highly silicon‐doped stable heterofullerenes, that the silicon dopants must be completely isolated from each other by means of strong C═C double bonds. Here, linking the germanium substitutions together is an applicable strategy for obtaining highly doped stable isolated heterofullerenes since it avoids weak heteroatom─heteroatom bonds. Therefore, none of the computed heterofullerenes collapses to open, to deform, or to segregate fullerenic cages. As to band gaps (ΔE_HOMO‐LUMO), and nucleus‐independent chemical shifts at cage centers (NICS (0)), C₁₄Ge₆‐2 immerges with the highest value. Hence, it is predicted to be the most stable against electronic excitation. It contains 2 Ge─Ge single bonds at the cap‐equatorial positions. On the other hand, as to zero‐point vibrational energy and heat of atomization (ΔH_at), C₁₄Ge₆‐8 appears with the lowest and highest value, respectively. It contains 6 alternating germanium atoms in the equatorial and cap positions. Thus, it is predicted to be the most thermodynamically stable. So, germanium substitution leads to a high charge distribution on the surfaces of all the isomers specially C₁₄Ge₆‐9 with +1.496 charged germanum atoms. C₁₄Ge₆ isomers seem to be a good candidate for the hydrogen storage material.     

Theoretical study on C100 fullerenes and C96X4 (X=N,P, B,Si)

The geometrical structures and electronic properties of six fullerene isomers of C₁₀₀ were studied at the HF/6-31G^? and B3LYP/6-31G^? levels, respectively. The results of the fully optimized calculations show that three C₁₀₀ isomers 449:D₂, 425:C₁ and 442:C₂ are near isoenergetic isomers. The energies and properties of C₁₀₀ hexaanions were calculated. The C₁₀₀^6? (450:D₅) isomer is predicted to be the most stable isomer at the B3LYP/6-31G^? level, and the C₁₀₀^6? (449:D₂) isomer is 44.1 kcal/mol higher in energy. The heterofullerenes C₉₆X₄ (X=N, P, B, Si) formed from the initial C₁₀₀ (449:D₂) have also been investigated at the B3LYP/6-31G^? level. The HOMO–LUMO gaps and aromaticities show that the replacement of fullerene carbon atoms with four heteroatoms can enhance the electronic stabilization of C₁₀₀ (449:D₂).     

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.     

Electronic structure and enhanced visible‐light absorption of N,B‐codoped TiO2

We present GGA+U calculations to investigate the electronic structure and visible‐light absorption of N,B‐codoped anatase TiO₂. The N_sB_i (substitutional N, interstitial B) codoped TiO₂ produces significant Ti 3d and N 2p mid‐gap states when the distance of N and B atoms is far, whereas the N_iB_i (interstitial N and B) and N_sB_s (substitutional N and B) codoped TiO₂ prefer to form localized p states at 0.3–1.2 eV above the valence band maximum. Further, the optical band edges of the three codoped systems shift slightly to the visible region, but only the far‐distance N_sB_i codoped TiO₂ clearly shows an optical transition. These results indicate that N_sB_i codoped TiO₂ has a dominant contribution to the optical absorption of N,B‐codoped TiO₂. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electronic structure and the infrared absorption and Raman spectra of the semiconductor clusters C24, B12N12, Si12C12, Zn12O12, and Ga12N12

The optimized configurations, electronic structures, charge transfers, band gaps, total energies, cohesive energies, electron density maps, infrared absorption spectra, Raman spectra, and relevant modes of natural acoustic vibrations for the semiconductor clusters C₂₄, B₁₂N₁₂, Si₁₂C₁₂, Zn₁₂O₁₂, and Ga₁₂N₁₂ are calculated using the ab initio Hartree-Fock method in the 6–31G basis set. Original Russian Text ? V.V. Pokropivny, L.I. Ovsyannikova, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 3, pp. 535–542.     

Structural,magneto and optical properties of BX − 1NXC and BXNX − 1C cages (X = 12, 24 and 36)

The effect of carbon doping on the structural, optical and magneto properties of the B_XN_X cages has been studied using the B3LYP/6-31G^* level of density functional theory. With replacing one B or N atom with one C atom on the B_XN_X cages, the structural and symmetric properties, the optical absorption spectra and the band gaps of the B_XN_X cages change and the B_XN_X cages become magnetic. Our calculations conclude that the B_{X ? 1}N_XC and B_XN_{X ? 1}C cages can be interesting candidates for application in optoelectronics and spintronics.     

Tuning the electronic properties of the fullerene C<Subscript>20</Subscript> cage via silicon impurities

The fullerene C₂₀ represents one of the most active classes of nanostructures, and they have been widely used as active materials for important applications. In this study, we investigate and discuss the tuning of the electronic properties of the fullerene C₂₀ cage via various consternations and locations of silicon atoms. All calculations are based on the density functional theory (DFT) at the B3LYP/3-21G level through the Gaussian 09W program package. The optimized structures, density of state (DOS) analysis, total energies, dipole moments, HOMO energies, Fermi level energies, LUMO energies, energy gaps, and the work functions were performed and discussed. Our results show that the electronic properties of C₂₀ cage do not only depend on the silicon impurity concentrations, but also depend on the geometrical pattern of silicon impurities in the C₂₀ cage. The tuning of the electronic properties leads to significant changes in the charge transport and the absorption spectra for C₂₀ cage via engineering the energy gap. So, we suggest that substitutional impurities are the best viable option for enhancement of desired electronic properties of C₂₀ cage for using these structures in nanoelectronics and solar cell applications.     

Structures,stabilities and electronic properties of boron-doped silicon clusters B3Sin (n=1–17) and their anions

The structures, stabilities and electronic properties of neutral and anionic B₃Si_n (n?=?1–17) clusters have been systemically investigated on the basis of density functional theory at the B3LYP/6-311?+?G(d) level and CALYPSO structure prediction method. The structural searches show that three boron atoms tend to form B₃ triangle encapsulated into Si_n cages with the increasing number of silicon atoms. Most of the lowest energy structures can be derived by using the squashed pentagonal bipyramid structure of B₃Si₄ and B₃Si₄^? as the major building unit. The relative stabilities are studied based on the calculated binding energies, second-order difference of energies and HOMO–LUMO gaps of the lowest energy structures. In addition, Hirshfeld, natural population analysis, Bader approaches and natural electronic configuration are performed to explore the charge transfer. At last, molecular orbital, magnetic properties, IR, Raman and UV–vis spectra are also, respectively, analysed for providing strong support for essential theoretical and experimental research.     

内掺过渡金属非典型富勒烯M@C22(M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni) 几何结构、电子结构、稳定性和磁性的密度泛函研究

采用密度泛函理论中广义梯度近似对非典型富勒烯C₂₂和过渡金属内掺衍生物M@C₂₂(M=Sc,Ti,V,Cr,Mn,Fe,Co和Ni)的几何结构和电子结构进行计算研究.发现非典型富勒烯C₂₂的基态结构是含有一个四碳环的单重态笼状结构.过渡金属原子的掺入明显提高了体系的稳定性. C-M键既有一定共价性又有一定离子性.磁性、能级图、轨道分布和态密度图分析表明: M原子的3d轨道和碳笼的C原子的原子轨道之间存在较强的轨道杂化. Ti, Cr, Fe和Ni内掺的结构出现磁性完全猝灭现象. Sc和碳笼间是弱反铁磁作用, V,Mn和Co与碳笼间是弱铁磁作用.     

Structure,electronic and magnetic properties of hexagonal boron nitride sheets doped by 5d transition metal atoms: First-principles calculations and molecular orbital analysis

A first-principles calculation based on density functional theory is carried out to reveal the geometry, electronic structures and magnetic properties of hexagonal boron nitride sheets (h-BNSs) doped by 5d transitional mental atoms (Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) at boron-site (B_5d) and nitrogen-site (N_5d). Results of pure h-BNS, h-BNS with B vacancy (V_B) and N vacancy (V_N) are also given for comparison. It is shown that all the h-BNSs doped with 5d atoms possess a C_3v local symmetry except for N_Lu and N_Hg which have a clear deviation. For the same 5d dopant, the binding energy of B_5d is larger than that of N_5d, which indicates the substitution of a 5d atom for B is preferred. The total densities of states are presented, where impurity energy levels exist. Besides, the total magnetic moments (TMMs) change regularly with the increment of the 5d atomic number. Theoretical analyses by molecular orbital under C_3v symmetry explain the impurity energy levels and TMMs.     

Conformational energies of silacyclohexanes C5H10SiHMe,C5H10SiH(CF3) and C5H10SiCl(SiCl3) from variable temperature Raman spectra

From variable temperature vibrational Raman spectra, the axial/equatorial enthalpy differences for the substituted silacyclohexanes C₅H₁₀SiHMe, C₅H₁₀SiH(CF₃) and C₅H₁₀SiCl(SiCl₃) were determined. The pure liquids and solutions in various solvents were investigated. Preferred conformations are equatorial for methylsilacyclohexane and axial for trifluoromethylsilacyclohexane, consistent with earlier results from nuclear magnetic resonance experiments and ab initio calculations. For C₅H₁₀SiCl(SiCl₃) an enthalpy difference close to zero was found, which is supported by high‐level which is supported by high‐level quantum chemical calculations at the second‐order Møller‐Plesset (MP2) and coupled cluster with single, double, and perturbative triple excitations (CCSD(T)) levels, which employed various basis sets. A novel synthesis for C₅H₁₀SiCl(SiCl₃) was developed using ClMg(CH₂)₅MgCl instead of BrMg(CH₂)₅MgBr as a starting material. The procedure avoids the formation of partially brominated products, facilitating the purification of the compound. ¹H, ¹³C and ²⁹Si nuclear magnetic resonance data are reported. Copyright © 2012 John Wiley & Sons, Ltd.     

Chiral structures and tunable magnetic moments in 3d transition metal doped Pt6 clusters

The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt6 （M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn） are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital （HOMO） lowest unoccupied molecular orbital （LUMO） gaps suggest that the doped clusters can have higher chemical activities than the pure Pt7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt6 clusters is from 0 μB to 7 μB, revealing that the MPt6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties.     

C60富勒烯-巴比妥酸及其二聚体几何结构和电子结构的密度泛函计算研究

采用基于密度泛函理论的广义梯度近似,对C₆₀富勒烯-巴比妥酸及其二聚体的几何结构和电子结构进行了计算研究.发现：C₆₀富勒烯-巴比妥酸只有一种稳定结构,且掺杂巴比妥酸基团对C₆₀分子构型的影响是局域的.C₆₀富勒烯-巴比妥酸的二聚体有三种同素异构体,分别以［6,5］—［6,5］,［6,6］—［6,5］和［6,6］—［6,6］三种方式键合,从能隙大小顺序和总能相对大小来看,［6,6］—［6,6］结构最为稳定.电子结构方面,在C₆₀富勒烯-巴比妥酸单体中,Donor-Acceptor电荷转移体系为C₆₀富勒烯-巴比妥酸,即电荷是从C₆₀向巴比妥酸转移.由前线轨道和自旋布居数得知,C₆₀富勒烯-巴比妥酸单体很好地保留了C₆₀的电磁性质,但稳定性下降,易发生二次加成反应形成二聚体.对于C₆₀富勒烯-巴比妥酸二聚体,Mulliken电荷分析显示,在加成四元环处的碳原子分别得到0104e和0106e电荷,而与它们邻近的碳原子则失去电子,带有正电荷,且距加成位置越近的碳原子失去的电荷越多.在远离加成位置处,碳原子的净电荷变化相对较小.与单体152eV能隙相比,二聚体中的能隙为1.45eV.其前线轨道分布与单体相比,最高占据轨道几乎未变,但最低未占据轨道发生了很大变化. 关键词： 几何结构 电子结构 密度泛函     

Theoretical study on the sequential hydroxylation of C82 fullerene based on Fukui function

In the present work semi-empirical PM3 method and ab initio density-functional theory calculations were performed in carbon systems. The condensed Fukui function was calculated and HOMO–LUMO were visualised in order to study the sequence of hydroxylation of two isomers of C₈₂ fullerene for the low coverage regime, with the formula C₈₂(OH) _x where x?=?0???12. It was found that there was a formation of dangling bonds on structures with an odd number of hydroxyl groups on the fullerene surface, which suggests an enhanced reactivity of these molecules. Nevertheless, the coverings with an even number of groups tend to the reconstruction of π bonds, obtaining less reactive molecular structures. With the adsorption of the first group, a narrow HOMO–LUMO gap (1.28?eV) is observed in comparison with the C₈₂(OH)₂ system (1.70?eV), as is found in similar systems, such as C₆₀ fullerenol [E.E. Fileti et al., Nanotechnology 19, 365703 (2008); J.G. Rodríguez-Zavala and R.A. Guirado-López, Phys. Rev. B 69, 075411 (2004)]. Through an analysis of the electronic structure to these coverings, a splitting of electronic energy levels in the structure with one hydroxyl group is observed, which could be one of the factors that causes the narrowing of the energy gap in this structure. On the other hand, with a coverage of 12 hydroxyl groups, the formation of an amphiphilic molecule, where the location of groups in one side of the C₈₂ surface provides an hydrophilic character, is observed, while the uncovered part has an hydrophobic character. This could be important in the formation of Langmuir monolayers. Finally, it is shown that the precise distribution of the OH groups on the fullerene surface plays a crucial role in the electronic structure of the polyhydroxylated fullerenes.     

密度泛函理论计算内掺氢分子富勒烯H2＠C60及其二聚体的几何结构和电子结构

采用密度泛函理论中的广义梯度近似(generalized gradient approximation,简称GGA),对内掺氢分子富勒烯H₂＠C₆₀及其二聚体的几何结构和电子结构进行了计算研究.发现无论是在H₂＠C₆₀单体,还是在其二聚体中,氢倾向以分子形式存在于碳笼中心处,且在室温下氢分子可以做自由旋转.电子结构分析表明,氢分子掺入到C₆₀和C₁₂₀中,仅对距离费米能级以下-8eV至-5eV能级处有一定的贡献,其他能级的分布和能隙几乎没有变化. 关键词： 几何结构 电子结构 密度泛函     

Adsorption of NH3 and NO2 molecules on C48B6N6 heterofullerene: A DFT study on electronic properties

Adsorption of NH₃ and NO₂ molecules on the external surface of C₄₈B₆N₆ heterofullerene is investigated using DFT method. Attachment of NH₃ and NO₂ on C₄₈B₆N₆ heterofullerenes are compared with the bare C₄₈B₆N₆ model optimized at the B3LYP/6-31G^? level. The high surface binding energies indicates that ammonia undergoes chemical adsorption and could be compatible with the long recovery time but C₄₈B₆N₆ should be good NO₂ sensors with quick response as well as short recovery time. Total (TDOS) and partial (PDOS) density of state calculations is also considered to elucidate the difference in the NH₃ and NO₂ gas detection mechanism of C₄₈B₆N₆. The overlap population density of state (OPDOS) indicated that the chemical adsorption is due to the overlap of atomic orbitals below the Fermi level. The calculated results suggest that the C₄₈B₆N₆ heterofullerene is a suitable sensor material for NO₂ and is an ideal material for elimination and filtering of ammonia.     

Microwave spectrum, molecular structure, dipole moment, and theoretical calculation of cyclopentanone oxime

The microwave spectra of cyclopentanone oxime (C₅H₈NOH) and its deuterated species (C₅H₈NOD) were observed in the frequency region from 9 to 40 GHz. Only a-type R-branch transitions were assigned in the vibrational ground and excited states. The rotational constants of normal species were determined to be A = 5870.80(33), B = 1917.021(8), and C = 1526.784(8) MHz in the vibrational ground state, and A = 5870.16(43), B = 1842.707(9), and C = 1479.401(9) MHz for deuterated species. The dipole moments were determined as μ_a = 0.80(10), μ_b = 0.20(10), and μ_c = 0.40(10) D. The ring-puckering vibrational states were observed up to v = 6. The vibrational mode was nearly harmonic. The fundamental frequency of the ring-puckering mode was found to be 70(20) cm⁻¹. The molecular structure of cyclopentanone oxime was determined to be a twisted configuration by comparing the observed and calculated rotational constants, planar moment of inertia, P_cc, and r_s coordinates of the hydroxyl hydrogen atom. On the molecular geometry, the bond angle, C₂C₁N₆ (Fig. 1), is larger than C₅C₁N₆ by ca. 6°, because of the steric repulsion between the methylene group of C₂ atom and hydroxyl group.     

Geometry of C2N2 + and HCN+ from low-energy photoelectron spectroscopy

Quantitative Franck-Condon calculations are applied to the first two band systems of the low energy photoelectron spectrum of dicyanogen (C₂N₂) and to the first band system of hydrogen cyanide. Estimates are made of the bond length changes from the ground electronic state of the molecule to various states of C₂N₂ ⁺ and to the ground state of HCN⁺. These changes are consistent with expectations based on simple molecular orbital theory.

It is shown that there is sufficient intensity in the perturbed first system of HCN, and also that of DCN, to account for an overlapping second system due to the removal of an electron from the 5σ orbital.     

Encapsulation of small fullerenes into nitrogenated holey nanotubes: a density functional theory study

Encapsulation of fullerene into nanotubes based on a C₂N sheet, known as nitrogenated holey graphene, was investigated using density functional theory. The structural and electronic properties of these carbon hybrid materials, consisting of nitrogenated holey nanotubes and a small C₂₀ fullerene, were studied. The formation energies showed that encapsulation of the fullerene into the nitrogenated holey nanotube is an exothermic process. To characterise the electronic properties, the electronic band structure and density of states of armchair and zigzag nitrogenated holey nanotubes were calculated. Filling these nanotubes with the C₂₀ fullerene resulted in a p-type semiconducting character. The energy band gap of the nitrogenated holey nanotubes decreased with fullerene encapsulation. The results are indicative of the possibility of band gap engineering by encapsulation of small fullerenes into nitrogenated holey nanotubes.