Rh在单壁碳纳米管上吸附的密度泛函理论研究

本文利用密度泛函理论研究了Rh原子在（6,6）单壁碳纳米管内外的吸附行为. 通过对Rh在单壁碳纳米管上不同吸附位的吸附构型与吸附能的研究发现: Rh吸附在管内、外的洞位最稳定, 且管外吸附比在管内强. 这是由于单壁碳纳米管的卷曲效应使得管外电荷密度比管内大造成的. 态密度分析表明, 吸附在管内外的Rh原子的5s电子均转移到了4d轨道上; Rh原子4d轨道上的电子转移到了（6, 6）碳管上, 使Rh带正电, 碳管带负电. 结合能带分析表明, Rh原子吸附在管内磁性较弱, 而吸附在管外较强. 关键词： 密度泛函理论 单壁碳纳米管 Rh原子 吸附     

1,2,3-三氮杂苯-水复合物氢键相互作用

用密度泛函理论在B3LYP/6-31 G**水平上对1,2,3-三氮杂苯和水形成1:1、1:2和1:3复合物的基态氡键结构进行几何优化和性质计算．计算结果表明,复合物之间存在较强的氢键作用．所有稳定复合物结构中形成一个N…H-O氢键并终止于O…H-C氢键的氢键水链构型最稳定．氢键的形成是水分子中H-O键振动频率减小(红移)．NBO分析表明,最稳定的1:1、1:2和1:3复合物发生分子间电荷转移总量分别为0．0222e、0．0261e和0．0273e．同时,用含时密度泛函理论方法在TD-B3LYP/6-31 G**水平计算了1,2,3-三氮杂苯单体及其氢键复合物的第一1(n,π*)激发态的垂直激发能．     

锯齿型单壁碳纳米管的广义层错能计算

基于密度泛函理论的第一性原理方法,计算了两种不同半径的锯齿型单壁碳纳米管以及单层石墨的广义层错能曲线。对小位移处广义层错能曲线进行斜率拟合所得切变模量与其它文献值一致。对三条广义层错能曲线的对比可知,锯齿型碳纳米管与单层石墨的广义层错能曲线相近,锯齿型单壁碳纳米管的曲率效应不明显。     

亲水性两性离子聚合物刷的构象与结构

本文应用分子场理论,研究暴露于水蒸气中的亲水性两性离子聚合物(HP)刷的构象与结构.理论模型考虑HP-水(P-W)氢键和水-水(W-W)氢键效应,以及HP单体之间的偶极-偶极相互作用.研究发现,P-W与W-W氢键决定着HP的水合性,P-W氢键形成,会诱导HP刷溶胀.我们通过考察HP单体间的偶极-偶极相互作用发现,随着偶极-偶极相互作用增强,HP链在垂直培基表面沿着链方向,形成了结节状结构.这是由于HP单体之间的偶极-偶极静电吸引作用导致单体间汇聚结节,这种结节在刷内产生了较强的排斥体积作用,因此,这种HP刷具有抗污性能.在较高的接枝密度环境下,由于HP链间单体之间的偶极-偶极静电吸引作用,会形成链间单体-单体的结节,在刷内形成结节网络状凝胶结构,这种结构的出现,会使得HP刷呈现极强的抗污性.另外,当体系中水蒸气浓度增加、水合相互作用增强时,增加的P-W氢键将平衡HP单体之间的偶极-偶极相互作用,使得结节解开,聚合物链伸展.我们的理论结果符合实验观测,由此表明,P-W氢键效应,以及HP单体之间的偶极-偶极相互作用决定着HP刷的构象转变和结构特性,刷内出现的两性离子聚合物链内单体间的结节和链间单体结节状凝胶结构,是两性离子聚合物刷呈现较强抗污性的本质特性.     

Ni原子链填充碳纳米管的能量、电子结构和磁性的第一性原理计算

在广义梯度近似(GGA)下,利用密度泛函理论(DFT)框架下的第一性原理投影缀加波(PAW)赝势方法,研究了单根Ni原子链填充扶手椅型(n,n)(5≤n≤9)单壁碳纳米管的能量、电子结构和磁性.结果表明(5,5)碳纳米管直径过小排斥Ni原子链的插入,(6,6)碳纳米管是容纳Ni原子链的最小碳纳米管,特别是Ni原子链位于其中心轴线上时的形成能最低.以Ni@(6,6)和Ni@(7,7)系统为例,计算并分析了其自旋极化能带结构,电子总态密度,分波态密度和磁性,发现Ni原子的3d态电子 关键词： Ni原子链 碳纳米管 电子结构 磁性能     

水蒸气诱导两性离子聚合物刷的构象转变

我们把Flory Huggins模型(association models)推广应用到暴露于水蒸气中的两性离子聚合物刷体系,考虑两性离子聚合物-水氢键(P-W氢键)与两性离子聚合物链间两亲离子单体-单体键合(zwitterions complex)、形成氢键与两性离子聚合物链构象的耦合特性,研究水蒸气诱导的两性离子聚合物刷构象转变的机理和相行为.研究发现,随着水蒸气浓度的增加,P-W氢键效应会使得两性离子聚合物刷溶胀;两亲离子单体-单体键合效应会导致水分子将会被排出刷外,并会导致两性离子聚合物刷塌缩.通过分析两性离子聚合物刷的相图发现,P-W氢键效应在决定两性离子聚合物刷的相行为中起到主导作用,在水蒸气增加过程中两性离子聚合物刷将会单调溶胀.基于本文的分析,可以预言,由于P-W氢键效应,两性离子聚合物刷可以吸附水蒸气,当两性离子聚合物链接枝密度足够高时,两性离子聚合物刷内的水分子将会被排出,并会形成两亲离子单体-单体键合连接的凝胶状结构.     

非迭代冻结密度近似方法在计算氢键相互作用的合理性研究

为计算相互作用较弱的分子碎片之间的耦合能,Harris从密度泛函理论出发,提出了一种简化方法,即冻结密度近似(FDA)方法.对该方法在描述分子间氢键作用的合理性进行了验证.对水分子间的HO┉H氢键、甲酰胺与水分子间的NH┉O氢键、二氟甲烷和水分子间的OH┉F氢键,以及DNA中的碱基(AT,GC)之间的N—H┉O,N—H┉N等类型的氢键的计算表明:若电子交换关联采用非定域自旋密度近似,FDA的计算结果同其他abinitio方法的计算结果以及实验结果都符合得很好.FDA在计算过程中既不需要求解泊松方程,也不需要进行反复的自洽迭代,所以运算速度较快,在研究生物大分子体系中的氢键相互作用方面具有一定的使用价值 关键词： 冻结密度近似 氢键 密度泛函     

半导体性单壁碳纳米管与其石墨衬底表面相互作用的第一性原理计算

利用基于密度泛函理论的计算方法,研究了处于石墨（HOPG）表面的半导体性单壁碳纳米管,发现碳纳米管下面的石墨受碳管的作用向下凹陷,而纳米管本身虽然保持其形状不变,但它的电子态受石墨衬底影响,造成导带下移,禁带宽度明显减小. 关键词： 单壁碳纳米管 密度泛函理论 局域密度近似方法     

乙醇-水分子团簇(C2H5OH)nH2O(n=1-4)的稳定结构特性研究

采用密度泛函理论M06-2X方法, 在6-311 ++G(2d,2p)// 6-311 ++G(d,p)基组水平上对乙醇-水分子团簇(C2H5OH)nH2O(n=1-4)进行计算, 得到乙醇-水分子团簇的各种稳定构型, 并对乙醇水分子团簇的结构特点进行了分析, 优化的各种低能结构、结构参数、氢键、结合能、平均氢键参数、NBO电荷分布等．结果表明: 最低能稳定结构都是环状的, 而且这些团簇除了形成O―H…O型主氢键外, 还有另一种作用方式C―H…O, 称之为次氢键．虽然C―H…O氢键远弱于O―H…O氢键, 但是对团簇的某些性质也有一定的影响.     

乙醇-水分子团簇(C2H5OH)nH2O(n=1-4)的稳定结构特性研究

采用密度泛函理论M06-2X方法, 在6-311 ++G(2d,2p)// 6-311 ++G(d,p)基组水平上对乙醇-水分子团簇(C2H5OH)nH2O(n=1-4)进行计算, 得到乙醇-水分子团簇的各种稳定构型, 并对乙醇水分子团簇的结构特点进行了分析, 优化的各种低能结构、结构参数、氢键、结合能、平均氢键参数、NBO电荷分布等．结果表明: 最低能稳定结构都是环状的, 而且这些团簇除了形成O―H…O型主氢键外, 还有另一种作用方式C―H…O, 称之为次氢键．虽然C―H…O氢键远弱于O―H…O氢键, 但是对团簇的某些性质也有一定的影响.     

Stable single helical C-and I-chains inside single-walled carbon nanotubes

The helicity of stable single helical carbon chains and iodine chains inside single-walled carbon nanotubes(SWCNTs)is studied by calculating the systematic van der Waals interaction energy.The results show that the optimal helical radius increases linearly with increasing tube radius,which produces a constant separation between the chain structure and the tube wall.The helical angle exhibits a ladder-like decrease with increasing tube radius,indicating that a large tube can produce a small helicity in the helical structures.     

Interaction between methanol and single-walled carbon nanotubes: Density functional theory study

Density functional calculations have been performed to investigate the dependence of methanol interaction with the side walls of single-walled carbon nanotubes (SWCNTs) on the nanotube's type, curvature and chirality. The author's results show that methanol prefers to be physically adsorbed on semiconducting CNTs in comparison with the metallic one. It was found that the binding energy of methanol is increased for adsorption on larger-diameter nanotubes. Furthermore, we find that when a methanol molecule was adsorbed on higher chiral angle nanotubes the binding energy was increased. The study of the electronic structures and Mulliken analysis indicate that the methanol and CNT are interacting rather weakly, consistent with recent experimental observation.     

Theoretical Studies on Interaction Between Methanol and Functionalized Single-Walled Carbon Nanotubes

We study the adsorption of a methanol molecule on single-walled carbon nanotubes (SWCNTs) with various diameters and chiral angles by using the density functional theory based calculations. We find that methanol prefers to be adsorbed physically on the exterior surface of chiral nanotubes in comparison to the armchair and zigzag tubes with binding energy of about-2.76 kcal/mol, which is consistent with recent experimental andtheoretical investigation results. We further consider the adsorption of methanol on the exterior surface and edge site of functionalized SWCNTs. The obtained results indicate that the binding energy of methanol is significantly increased for adsorption on the sidewall of functionalized nanotubes. It is also found that the adsorption of methanol at the edge site of both functionalizedand pristine SWCNT is remarkably different (chemisoption process) incomparison to the exterior sidewall of the tubes. Furthermore, the electronic structures and Mulliken charge population of the considered complexes at their ground state are discussed within the context.     

Electronics and Structural Properties of Single-Walled Carbon Nanotubes Interacting with a Glucose Molecule：ab initio Calculations

The adsorption of glucose molecule on single-walled carbon nanotubes (SWCNTs) is investigated by density functional theory calculations. Adsorption energies and equilibrium distances are evaluated, and glucose binding to the typical semiconducting and metallic nanotubes with various diameters and chirality are compared. We also investigated the role of the structural defects on the adsorption capability of the SWCNTs. We could observe larger adsorption energies for the larger diameters semiconducting CNTs, while the story is paradoxical for the metallic CNTs. The obtained results reveal that the adsorption energy is significantly higher for nanotubes with higher chiral angles. Finally, the adsorption energies are calculated for defected nanotubes for various configurations such as glucose molecule approaching to the pentagon, hexagon, and heptagon sites in the tube surface. We find that the respected defects have a minor contribution to the adsorption mechanism of the glucose on SWNTs. The calculation of electron transfers and the density of states supports that the electronic properties of SWCNTs do not change significantly after the gluycose molecular adsorption. Consequently, one can predict that presence of glucose would neither modify the electronic structure of the SWCNTs nor direct to a change in the conductivity of the intrinsic nanotubes.     

Electronics and Structural Properties of Single-Walled Carbon Nanotubes Interacting with a Glucose Molecule: ab initio Calculations

The adsorption of glucose molecule on single-walled carbon nanotubes(SWCNTs)is investigated by density functional theory calculations.Adsorption energies and equilibrium distances are evaluated,and glucose binding to the typical semiconducting and metallic nanotubes with various diameters and chirality are compared.We also investigated the role of the structural defects on the adsorption capability of the SWCNTs.We could observe larger adsorption energies for the larger diameters semiconducting CNTs,while the story is paradoxical for the metallic CNTs.The obtained results reveal that the adsorption energy is significantly higher for nanotubes with higher chiral angles.Finally,the adsorption energies are calculated for defected nanotubes for various configurations such as glucose molecule approaching to the pentagon,hexagon,and heptagon sites in the tube surface.We find that the respected defects have a minor contribution to the adsorption mechanism of the glucose on SWNTs.The calculation of electron transfers and the density of states supports that the electronic properties of SWCNTs do not change significantly after the gluycose molecular adsorption.Consequently,one can predict that presence of glucose would neither modify the electronic structure of the SWCNTs nor direct to a change in the conductivity of the intrinsic nanotubes.     

Strange non-chaotic attractors in a state controlled-cellular neural network-based quasiperiodically forced MLC circuit

The adsorption energies, bond order, atomic charge, optical properties, and electrostatic potential of nitrogen molecules of armchair single-walled carbon nanotubes (SWCNTs) and nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) were investigated using density functional theory (DFT). Our results show that adsorption of the \(\hbox {N}_{2}\) molecules on the external wall of a nanotube is more effective than on the internal wall in SWCNTs. The results show that \(\hbox {N}_{2}\) molecule(s) are weakly bonded to SWCNTs and N-SWCNTs through van der Waals-type interactions. The interaction of \(\hbox {N}_{2}\) molecules with SWCNTs and N-SWCNTs is physisorption as the adsorption energy and charge transfer are small, and adsorption distance is large. The electronic transitions from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) (\(\hbox {H}\rightarrow \hbox {L}\)) have the maximum wavelength and the lowest oscillator strength. The potential sensor on the surface of pristine SWCNTs and N-SWCNTs for the adsorption of \(\hbox {N}_{2}\) molecule(s) is investigated. The N-loaded single-walled carbon nanotube is introduced as a better \(\hbox {N}_{2}\) molecule(s) detector when compared with SWCNTs.     

Modeling double-helix carbon chains inside single-walled carbon nanotubes: Stable structures and XRD analysis

Atomic models are applied to investigate quasi-one-dimensional composites. The study presents the theoretical prediction of stable double-helix carbon chains growing inside single-walled carbon nanotubes as a function of tube radius. Meanwhile, our analysis shows that metastable structures may co-existence with the stable one, for small tubes. The classical molecular dynamics simulation shows that the regular and distorted double-helix C-chains are obtained with the tube's diameter smaller and larger than 13.32 Å, respectively. The temperature plays a minor role in the stable carbon chain structure unit it increases to 2500 K. The geometry optimization and the electronic structural analysis of the obtained optimal structure by the DFT calculation further justify our classical force field analysis. The electronic structure of SWCNTs can be significantly modified by the inserted carbon chain. The orbital hybridization between the host-guest molecules plays a key role in stabilizing the encapsulated double-helix carbon chain. Finally, X-ray powder diffraction (XRD) patterns of stable helical structures inside armchair tubes are presented for guidance of future experimental analyses.     

单壁碳纳米管弹性性质的羟基接枝效应

用分子动力学方法研究了端口接枝不同数量羟基对扶手椅型和锯齿型单壁碳纳米管弹性模量的影响.结果表明,未接枝的扶手椅型(5, 5),(10,10)管和锯齿型(9, 0),(18, 0)管杨氏模量分别为948,901和804,860GPa.在接枝2—8个羟基情况下,锯齿型单壁碳纳米管拉伸杨氏模量基本不随接枝数量增加发生变化,而扶手椅单壁碳纳米管则不同,接枝状态下的弹性模量比未接枝状态小很多,但接枝一定数量后,其杨氏模量又略增到某一稳定值.分别从接枝后碳纳米管变形电子密度等值线结构、C—C键长和系统结合能变化规律等方面,对单壁碳纳米管弹性模量的接枝效应进行了分析. 关键词： 碳纳米管 羟基 接枝效应 杨氏模量