贵金属原子与点缺陷石墨烯的键增强作用

通过密度泛函理论研究了Ag、Au、Pt原子在完美和点缺陷(包括N掺杂、B掺杂、空位点缺陷)石墨烯上的吸附以及这些体系的界面性质.研究表明Ag、Au不能在完美的石墨烯上吸附,N、B掺杂增强了三种金属与石墨烯之间的相互作用.而空位点缺陷诱发三种金属在石墨烯上具有强化学吸附作用.通过电子结构分析发现,N掺杂增强了Au、Pt与C形成的共价键,而Au、Ag与B形成了化学键.空位点缺陷不仅是金属原子的几何固定点,同时也增加了金属原子和碳原子之间的成键.增强贵金属原子和石墨烯相互作用的顺序是:空位点缺陷>>B掺杂>N掺杂.     

铜族金属与完整及氮掺杂石墨烯的相互作用

基于广义梯度密度泛函理论和周期平板模型,研究了铜族金属单原子和双原子簇与完整及氮掺杂石墨烯的结合情况.结果表明,氮掺杂后石墨烯的电子结构特性由半金属性变为金属性;铜族金属在完整及石墨型氮掺杂石墨烯上的吸附较弱,结合能约为0.5eV,而在吡啶型氮掺杂和吡咯型氮掺杂石墨烯上有较强的化学吸附,结合能一般大于1eV;吡咯型氮掺杂后的构型不稳定,金属原子及簇与包含该结构的石墨烯衬底作用时会使其向吡啶型氮掺杂转变,并最终得到基于吡啶型氮掺杂的稳定吸附构型.Mulliken电荷布居分析显示,吸附在吡啶型氮掺杂石墨烯上的金属单原子与金属双原子簇带电性质相反.态密度及轨道分析表明,Cu与吡啶型氮掺杂石墨烯空位处留有悬挂键的三个原子成键,而Au与其中两个C原子成键.     

石墨烯中的单空位缺陷对铂原子催化解离氧分子的影响

采用密度泛函理论中的B3LYP方法研究了石墨烯中的单空位缺陷对铂原子(Pt)催化解离O_2分子的影响.计算发现O_2分子首先通过[2+1]或[2+2]环加成作用吸附在以单空位缺陷石墨烯为载体的Pt上(Pt-SV),并以不同的路径进行解离,吸附能分别为-158.23和-152.45kJ/mol.由于石墨烯片上单空位缺陷的存在,O_2分子更容易吸附在单空位缺陷处的Pt上,并且O_2在Pt-SV上解离的能垒(130.25kJ/mol)也明显比在Pt-pristine上解离的能垒低(76.23kJ/mol).因此石墨烯上单空位缺陷的存在提高增加了Pt的催化能力.     

ZnSe掺Cu与Zn空位缺陷的稳定性、电子结构与光学性质

采用基于密度泛函理论框架下的第一性原理平面波超软雁势方法, 对ZnSe闪锌矿结构本体、掺入p型杂质Cu(Zn_0.875Cu_0.125Se)及Zn空位(Zn_0.875Se)超晶胞进行结构优化处理. 计算并详细分析了缺陷体系的形成能和三种体系下ZnSe材料的态密度、能带结构、集居数、介电和吸收光谱. 结果表明: 在Zn空位与Cu掺杂ZnSe体系中, 由于空位及杂质能级的引入, 禁带宽度有所减小, 吸收光谱产生红移; 单空位缺陷结构不易形成, Zn_0.875Se结构不稳定, Cu掺杂ZnSe结构相对更稳定.     

缺陷石墨烯吸附Au、Ag、Cu的第一性原理计算

采用基于密度泛函理论的投影缀加波方法研究了Au、Ag、Cu吸附在缺陷石墨烯单侧和双侧的体系,对吸附体系的吸附能、磁性、电荷转移和电子结构进行了计算和分析.缺陷石墨烯吸附Au、Ag、Cu体系的吸附能比本征石墨烯增加2 eV以上,说明三种金属原子更容易吸附在缺陷位置;吸附体系的电荷密度差分和电子结构的结果表明,Au、Ag、Cu与缺陷石墨烯之间均为化学吸附.计算吸附体系的磁性发现,单侧吸附时三种吸附体系均有磁性,磁矩大约为1μB;双侧吸附时,三种吸附体系磁矩大约为2μB.     

缺陷石墨烯吸附Au、Ag、Cu的第一性原理计算

采用基于密度泛函理论的投影缀加波方法研究了Au、Ag、Cu吸附在缺陷石墨烯单侧和双侧的体系,对吸附体系的吸附能、磁性、电荷转移和电子结构进行了计算和分析. 缺陷石墨烯吸附Au、Ag、Cu体系的吸附能比本征石墨烯增加2 eV以上,说明三种金属原子更容易吸附在缺陷位置;吸附体系的电荷密度差分和电子结构的结果表明,Au、Ag、Cu与缺陷石墨烯之间均为化学吸附. 计算吸附体系的磁性发现,单侧吸附时三种吸附体系均有磁性,磁矩大约为1μ_B;双侧吸附时,三种吸附体系磁矩大约为2μ_B.     

杂原子掺杂的含单空位缺陷BN纳米管的非线性光学性质

采用密度泛函理论(DFT)研究了杂原子M(M=Li, Na, K, Be, Mg, Ca, C和Si)在B/N单空位缺陷处的掺杂对(6,0)BN纳米管体系非线性光学性质的影响. 采用B3LYP方法共得到了14种几何构型, 并采用BHandHLYP方法计算了这些结构的第一超极化率β₀值. 研究结果表明, 单纯的B或N缺陷几乎不影响BN纳米管体系的非线性光学性质; 与B缺陷处掺杂的体系相比, 杂原子在N缺陷处的掺杂更有利于提高BN纳米管体系的第一超极化率β₀值; 对于同周期掺杂原子, 还原性越强的原子掺杂对BN纳米管体系的第一超极化率β₀值的改善越明显, 表现为β₀(Ⅰ族)>β₀(Ⅱ族)>β₀(Ⅳ族); 对比同主族掺杂原子, 第三周期元素Na和Mg的掺杂能更有效地提高体系的第一超极化率β₀值, 原因主要在于原子半径和还原性等因素共同决定其对BN纳米管体系第一超极化率β₀值的改善程度. 本文研究结果为有效提高BN纳米管体系的非线性光学性质提供了一种新思路, 为基于BN纳米管的非线性光学材料设计提供了有价值的理论信息.     

脱质子化1,3环加成石墨烯外在固定位上的贵金属纳米线(英文)

为研究纳米线的形成机理,通过密度泛函理论(DFT)研究了贵金属(铂)在脱质子化1,3-环加成石墨烯上的吸附.研究发现:(1)吸附在1,3-环加成石墨烯上的铂原子引起该结构的脱质子化过程并形成脱质子化1,3-环加成石墨烯;(2)贵金属在脱质子化1,3-环加成石墨烯上的锚定位是氮原子邻位的碳原子,这在邻位碳原子的平均巴德电荷分析(高达1.0e)中得到进一步的证实;(3)铂原子在相邻的脱质子化吡啶炔单元上形成金属纳米线,并且该纳米线比相应的铂团簇稳定得多;(4)电子结构分析表明,铂的吸附并没有从根本上改变脱质子化1,3-环加成石墨烯的电子性质.铂金属的掺杂使得Pt6团簇吸附形成的复合物呈现金属性,而Pt6纳米线形成的复合物则为半金属性.     

氮掺杂单层石墨烯储钠性能的第一性原理研究

采用密度泛函理论(DFT)的第一性原理方法,对Na在本征石墨烯和不同掺杂浓度的N掺杂石墨烯(NG)表面的吸附性质进行了研究。确定了不同N掺杂浓度时NG的最稳定N分布结构,计算了Na在PG和不同掺杂浓度的NG表面的吸附能。计算结果表明,N原子掺杂倾向于取代对位或次临近位置的C原子;随着N掺杂浓度的增加,吸附高度逐渐增加,且与N掺杂分布相匹配;N掺杂浓度大于C∶N=2∶1(摩尔数比)时,Na在NG表面的吸附相对稳定,Na与C_9N_9表面的结合最稳定。     

Pt掺杂氧化石墨烯在酸性介质中催化氧还原反应DFT研究

目前Pt基催化剂被公认为是最高效的氧还原催化剂.我们采用了密度泛函理论研究了Pt掺杂5种不同氧化石墨烯和完美石墨烯在酸性环境中的氧还原反应机理,计算了氧还原反应中间体O₂、O、OOH、OH、H₂O和H₂O₂在不同掺杂石墨烯上的吸附性能、反应步骤与反应相对能量变化.结果表明,氧化石墨烯在O₂的活化、中间体吸附、掺杂难度（缺陷形成能）、能带带隙以及在反应中相对能量的降低都优于完美石墨烯,我们的工作将有助于为将来在实验中选择和合成氧还原催化剂提供一定的理论指导意义.     

DFT Study on the Effect of Hydrogen-bond Formation on the Adsorption of Aminotriazines on Graphene

DFT calculations have been performed to explore the aminotriazine adsorption on graphene surfaces.Relative energies,equilibrium geometries and electronic structures of monomer and dimer of aminotriazine molecules adsorbed at the surface were investigated and analyzed in details.It was found that the hydrogen atoms in the NH2 group of aminotriazine molecules are directed toward the graphene surface,and the adsorption energy increases as the NH2 group is added.The adsorbed aminotriazine molecules facilely form a dimer through the hydrogen bonding interactions,and the two aromatic rings of optimized structure of 2-amino-1,3,5-triazine(B) dimmer(denoted by B2) and melamine(D) dimmer(denoted by D2) are parallel to the graphene sheet.The large deviation of the averaged adsorption energy of B2 and D2 compared to monor adsorption may reflect the increase of π-π repulsion and the effect of hydrogen bond formation.The electronic structure analyses reveal that the formation of hydrogen bonds in melamine dimer has great influence on the adsorption mode at the graphene surface.     

Si-decorated graphene: a superior media for lithium-ions storage

The characteristics of lithium adsorption on Si-decorated graphene are investigated using first-principles density functional theory calculations. It is found that the Si atom is strongly adsorbed at the bridge site of the C–C bond with binding energy of about ?26.75 kcal/mol. We show that Si decorating turns Si:graphene complex into an electron-deficient system and significantly enhances the Li-storage capacity on the graphene. The obtained results indicate that up to eight Li-ions being adsorbed onto the Si-decorated graphene can form the stable complex. It is found, interestingly, that two Si atoms coated onto double-side of the graphene can strongly adsorb sixteen Li-ions. The analyses of electronic structures show a strong interaction between Li-ions and Si-decorated graphene leading to a high exothermicity. The stability of the sixteen Li-ions adsorbed on the Si:graphene system was evaluated with ab initio molecular dynamics simulation which have been carried out at room temperature. Our first-principles results are relevant to identify the potential applications of Si-decorated graphene as superior media for Li-ions storage.     

Direct Observation of Atomic Dynamics and Silicon Doping at a Topological Defect in Graphene

Chemical decoration of defects is an effective way to functionalize graphene and to study mechanisms of their interaction with environment. We monitored dynamic atomic processes during the formation of a rotary Si trimer in monolayer graphene using an aberration‐corrected scanning‐transmission electron microscope. An incoming Si atom competed with and replaced a metastable C dimer next to a pair of Si substitutional atoms at a topological defect in graphene, producing a Si trimer. Other atomic events including removal of single C atoms, incorporation and relocation of a C dimer, reversible C? C bond rotation, and vibration of Si atoms occurred before the final formation of the Si trimer. Theoretical calculations indicate that it requires 2.0 eV to rotate the Si trimer. Our real‐time results provide insight with atomic precision for reaction dynamics during chemical doping at defects in graphene, which have implications for defect nanoengineering of graphene.     

Application of Si‐doped graphene as a metal‐free catalyst for decomposition of formic acid: A theoretical study

Using density functional theory calculations, the adsorption and catalytic decomposition of formic acid (HCOOH) over Si‐doped graphene are investigated. For the stable adsorption geometries of HCOOH over Si‐doped graphene, the electronic structure properties are analyzed by adsorption energy, density of states, and charge density difference. A comparison of the reaction pathways reveals that both dehydration and dehydrogenation of HCOOH can occur over Si‐doped graphene. The estimated reaction energies and the activation barriers suggest that for the dehydration of HCOOH on the Si‐doped graphene, the rate‐controlling step is H + OH → H₂O reaction. For the dehydrogenation of HCOOH, the rate‐determining step is the breaking of the C? H bond of the HCOO group to form the CO₂ molecule and the atomic H. Our results reveal that the low cost Si‐doped graphene can be used as an efficient nonmetal catalyst for O? H bond cleavage of HCOOH. © 2015 Wiley Periodicals, Inc.     

Insights into hydrogen atom adsorption on and the electrochemical properties of nitrogen-substituted carbon materials

The nitrogen substitution in carbon materials is investigated theoretically using the density functional theory method. Our calculations show that nitrogen substitution decreases the hydrogen adsorption energy if hydrogen atoms are adsorbed on both nitrogen atoms and the neighboring carbon atoms. On the contrary, the hydrogen adsorption energy can be increased if hydrogen atoms are adsorbed only on the neighboring carbon atoms. The reason can be explained by the electronic structures analysis of N-substituted graphene sheets. Nitrogen substitution reduces the pi electron conjugation and increases the HOMO energy of a graphene sheet, and the nitrogen atom is not stable due to its 3-valent character. This raises an interesting research topic on the optimization of the N-substitution degree, and is important to many applications such as hydrogen storage and the tokamaks device. The electronic structure studies also explain well why nitrogen substitution increases the capacitance but decreases the electron conductivity of carbon electrodes as was experimentally observed in our experiments on the supercapacitor.     

Molecular orbital study for Na, Mg, and Al adsorption on the Si (111) surface

We investigated the interactions between the Si(111) surface and the Na, Mg, and Al atoms using cluster model calculations. Calculations were performed at levels of complete-active-space self-consistent-field (CASSCF) and multi-reference singly and doubly excited configuration interaction (MRSDCI) calculations using the model core potential method. Our calculations revealed that the most favorable sites of Na, Mg, and Al adsorption on Si(111) are on top (T₁), bridge (B₂), and 3-fold filled (T₄) sites, respectively. The nature of chemical bonds between these metal atoms and the dangling bonds of the surface Si atoms are found to be essentially covalent.     

Adsorption and diffusion on a phosphorene monolayer: a DFT study

A computational study of the adsorption and diffusion behavior of alkali and alkaline earth metal atoms on a phosphorene monolayer is reported. Our calculations were performed within the framework of density functional theory using the Perdew–Burke–Ernzerhof functional and projector augmented wave potentials, as derived from the generalized gradient approximation. Our binding energy calculations for various potential adsorption sites showed that the site located above the center of a triangle formed by three surface phosphorus atoms is the most attractive to all adatoms. In addition, simulation of the diffusion of adatoms across the surface of the phosphorene monolayer showed that the diffusion is anisotropic, with K having the lowest diffusion barrier (0.02 eV along the zigzag pathway). To the best of our knowledge, this is the lowest diffusion barrier of any metal adatom on a single layer of phosphorene. While phosphorene exhibited significantly better adatom adsorption and diffusion than graphene, it also showed a reduced storage capacity compared to graphene, most probably due to the structural distortion induced by the oversaturated phosphorene surface. This finding strongly suggests that a phosphorene–graphene hybrid system could be employed as a promising high-capacity ion anode.     

Effects of heteroatoms on the electronic,sensor, and adsorption properties of graphene

The effects of doping heteroatoms on the structure, electronic and adsorption properties of graphene are investigated using density functional theory calculations. Six different doped graphenes (with Al, B, Si, N, P, and S) are considered, and to obtain the interaction and adsorption properties, three sulfur-containing molecules (H₂S, SO₂, and thiophene) were interacted with selected graphenes. The adsorption energies (E _ad) in the gas phase and solvents show the exothermic interaction for all complexes. The maximum E _ad values are observed for aluminum doped graphene (AG) and silicon doped graphene (SiG), and adsorption energies in the solvent are not so different from those in the gas phase. NBO calculations show that the AG and SiG complexes have the highest E ⁽²⁾ interaction energies and simple graphene (G) and nitrogen doped graphene (NG) have the least E ⁽²⁾ energies. Population analyses show that doping heteroatoms change the energy gap. This gap changes more during the interaction and these changes make these structures useful in sensor devices. All calculated data confirm better adsorption of SO₂ by graphenes versus H₂S and thiophene. Among all graphenes, AG and then SiG are the best adsorbents for these structures.     

The chemisorption of coronene on Si(001)-2 x 1

Coronene (C24H12) adsorption on the clean Si(001)-2 x 1 surface was investigated by scanning tunneling microscopy and by density-functional calculations. The coronene adsorbed randomly at 25 degrees C on the surface and did not form two-dimensional islands. The scanning tunneling microscopy measurements revealed three adsorption sites for the coronene molecule on the Si(001) surface at low coverage. The major adsorption configuration involves coronene bonding to four underlying Si atoms spaced two lattice spacings apart in a dimer row. The two minor adsorption configurations involve asymmetrical bonding of a coronene molecule between Si dimer rows and form surface species with a mirror plane symmetry to their chiral neighbor species. The two minor bonding arrangements are stabilized by a type-C defect on the Si(001) surface.     

Enhancement of hydrogen physisorption on graphene and carbon nanotubes by Li doping

Density-functional calculations of the adsorption of molecular hydrogen on a planar graphene layer and on the external surface of a (4,4) carbon nanotube, undoped and doped with lithium, have been carried out. Hydrogen molecules are physisorbed on pure graphene and on the nanotube with binding energies about 80-90 meV/molecule. However, the binding energies increase to 160-180 meV/molecule for many adsorption configurations of the molecule near a Li atom in the doped systems. A charge-density analysis shows that the origin of the increase in binding energy is the electronic charge transfer from the Li atom to graphene and the nanotube. The results support and explain qualitatively the enhancement of the hydrogen storage capacity observed in some experiments of hydrogen adsorption on carbon nanotubes doped with alkali atoms.