不同构型石墨炔储氢性能的分子动力学比较研究

相关研究表明石墨炔是一种潜在的吸附储氢材料,然而石墨炔有不同的构型,不同构型石墨炔的储氢性能差异及原因尚未明晰。本研究基于分子动力学模拟,对α-GY、β-GY、γ-GY及GDY四种典型构型的石墨炔的吸氢性能进行了对比研究,分析了压力和温度对吸氢性能的影响,并剖析了吸氢性能差异的本质。研究发现β-GY和GDY两种构型的石墨炔吸氢性能在高压下优于其他两种构型,较低的温度有利于提高吸氢能力,而在较高压下提高压力对吸氢能力的影响不大;与石墨烯所要求高压相比,石墨炔在较低的压力下就可以实现高密度的氢气储存,例如α-GY在100 K的温度和0.5 MPa的压力下就可获得ω(H₂)=15.28的储氢密度,因此石墨炔有望成为一种性能更佳的吸附储氢材料。     

基于分子动力学的石墨炔纳米带空位缺陷的导热特性

空位缺陷石墨炔比完整石墨炔更贴近实际材料,而空位缺陷的多样性可导致更丰富的导热特性,因此模拟各种空位缺陷对热导率的影响显得尤为重要.采用非平衡分子动力学方法,通过在纳米带长度方向上施加周期性边界条件,基于AIREBO(adaptive intermolecular reactive empirical bond order)势函数描述碳-碳原子间的相互作用,模拟了300 K时单层石墨炔纳米带乙炔链上单空位缺陷和双空位缺陷以及苯环上单空位缺陷对其热导率的影响,利用Fourier定律计算热导率.模拟结果表明,对于几十纳米尺度范围内的石墨炔纳米带热导率,1)由于声子的散射集中和声子倒逆过程增强,与完美无缺陷的石墨炔纳米带相比,空位缺陷会导致石墨炔纳米带热导率的下降;2)由于声子态密度匹配程度高低的不同,相比于乙炔链上的空位缺陷,苯环的空位缺陷对石墨炔纳米带热导率影响更大,乙炔链上空位缺陷数量对石墨炔纳米带热导率的影响明显;3)由于尺寸效应问题,随着长度增加,石墨炔纳米带热导率会相应增大.本文的研究可为在一定尺度下进行石墨炔纳米带热导率的调控问题提供参考.     

α-碳锗炔稳定性及性质模拟

采用以量子力学为基础的半经验计算方法—–自洽和环境依赖的原子轨道线性理论,预测了类α-石墨炔的碳锗炔结构.研究了α-碳锗炔的稳定结构、电子结构以及热力学稳定性,得到其最稳定的构型是Ge原子在六元环的六个顶角处,晶格常数为8.686?的六角原胞构成的单层平面蜂窝状结构.该结构是带隙为1.078 e V的半导体.α-碳锗炔在很高的温度下都可以保持稳定,直到2280 K时其长程有序态才被破坏,当体系低于此温度时,可以通过降温使其恢复到零温时的稳定平面结构.     

$lt;i$gt;α$lt;/i$gt;-碳锗炔稳定性及性质模拟

采用以量子力学为基础的半经验计算方法–自洽和环境依赖的原子轨道线性理论,预测了类α-石墨炔的碳锗炔结构. 研究了α-碳锗炔的稳定结构、电子结构以及热力学稳定性,得到其最稳定的构型是Ge原子在六元环的六个顶角处,晶格常数为8.686 Å的六角原胞构成的单层平面蜂窝状结构. 该结构是带隙为1.078 eV的半导体. α-碳锗炔在很高的温度下都可以保持稳定,直到2280 K时其长程有序态才被破坏,当体系低于此温度时,可以通过降温使其恢复到零温时的稳定平面结构. 关键词： α-石墨炔')" href="#">α-石墨炔 α-碳锗炔')" href="#">α-碳锗炔 分子动力学模拟 热稳定性     

单原子作为保护基团实现石墨双炔纳米线的表面合成

由于在贵金属表面的双炔单元具有高反应活性,表面合成半导体性质的石墨双炔纳米线通常会受到副反应的严重影响,难以分立的纳米线的高质量制备.本文利用化学气相沉积1,4-bis(4-bromophenyl)-1,3-butadiyne分子到表面发生Ullmann偶联反应,可实现无支链的石墨双炔纳米线[-C≡C-Ph_2-C≡C-]_n (PYP)的高产率合成.进一步的单化学键分辨的非接触原子力显微镜表征揭示了单个金增原子与双炔键之间形成了π-ligand键,有效地充当了反应过程中双炔单元的保护基团,避免了偶联过程中的副反应,从而实现了分立的超长石墨双炔纳米线的合成.这项研究将启发对在表面反应中各类表面增原子所起保护作用的更深入研究.     

石墨炔管能带和力学性质的第一性原理研究

基于第一性原理计算,这篇文章研究了单壁锯齿型和扶手型石墨炔管的几何结构、电子结构以及杨氏模量.计算表明:石墨炔管是一类具有一定能隙的直接带隙半导体管,其带隙在0.4-1.3eV的能量范围,且随管径的增大而变小.而石墨炔管的杨氏模量在0.44-0.50Tpa区间变化.对于锯齿型石墨炔管,其杨氏模量随着半径的增大而变小而锯齿型石墨炔管的杨氏模量随其半径的增大而增大.     

理论研究过渡金属原子修饰石墨炔材料的功能性

采用基于密度泛函理论中第一性原理方法分别对石墨炔负载过渡金属原子(M-gra)体系的稳定构型以及对多种气体小分子的灵敏度和选择性进行理论研究.计算结果表明金属原子吸附在孔洞结构的H2位具有高稳定性,不同种类的金属原子能够有效调控石墨炔体系的电子特性和具有不同的磁矩.比较气体分子的吸附能大小,M-gra衬底对O和OH表现出高的灵敏度,单个NO、NO₂和O₂的稳定性高于CO分子.此外,小分子吸附的M-gra体系具有金属、半金属和半导体特性,在电子和气敏器件领域具有潜在应用.     

石墨炔管能带和力学性质的第一性原理研究北大核心CSCD

基于第一性原理计算,研究了单壁锯齿型和扶手型石墨炔管的几何结构、电子结构以及杨氏模量．计算表明：石墨炔管是一类具有一定能隙的直接带隙半导体管,其带隙在0．4～1．3eV的能量范围,且随管径的增大而变小．而石墨炔管的杨氏模量在0．44～0．50Tpa区间变化．对于锯齿型石墨炔管,其杨氏模量随着半径的增大而变小而锯齿型石墨炔管的杨氏模量随其半径的增大而增大．     

碳硅二炔结构及性质分子动力学模拟研究

采用基于量子力学的半经验哈密顿量的计算方法,即SCED-LCAO方法,模拟研究了碳硅二炔的稳定性结构、成键特点、电子结构等性质. 得出其最稳定的结构是单层平面结构,晶格常数为12.251 Å. 它通过 含有两个Si-C三键的链连接六元环构成. 这种平面结构在很大高温范围内都可以保持其稳定特性,直到1520 K时,该基本结构才被破坏,且结构中出现四元环. 体系温度低于1520 K时,均可通过降温,恢复其零温时的结构. 研究还发现这种共轭结构中Si,C 原子间存在稳定的sp杂化形式,对分布函数得出其键长为1.58 Å左右. 高温时sp杂化逐渐转变成其他杂化形式. 计算结果表明,在零温下,该电中性系统中存在离域π键,使得系统中的Si-C键长呈现平均化趋势. 研究表明,碳硅二炔的能隙为1.416 eV,LUMO,HOMO能级分别是0.386 eV和–1.03 eV表明了其n型半导体特性. 关键词： 碳硅二炔 分子动力学模拟 sp杂化 稳定性     

石墨狭缝中甲烷吸附的分子动力学模拟

用分子动力学模拟研究石墨狭缝中甲烷的吸附,考察狭缝宽度和温度对甲烷吸附的影响.模拟发现甲烷在石墨狭缝中出现分层现象,吸附层中甲烷具有类液特征,第一吸附层内甲烷中总有两个氢原子的连线与另外两个氢原子的连线分别位于平行于狭缝壁的两个平面内,游离层中甲烷呈现气体的特征;碳原子间的平均作用势说明吸附层中甲烷分子间结合能力大于游离层,吸附态是甲烷在石墨狭缝中的主要赋存形式之一;伦敦力以及由吸附层净电荷产生的电场力是甲烷吸附和分层的主要原因;甲烷的吸附量随狭缝宽度增大或温度升高而减少,当狭缝宽度小于16.46Å时,甲烷仅以吸附形态存在.甲烷在第一吸附层中的扩散能力最弱、游离层中最强,甲烷扩散系数随狭缝宽度的增大或温度的升高而增大.     

卤素驱动石墨二炔带隙的打开以实现光催化全解水

本文通过杂化密度泛函理论研究了卤素(F、Cl和Br)功能化的石墨二炔的能带结构. 结果表明修饰的石墨二炔的带隙能随着卤素原子对的增加而增加;同时,价带顶的位置受卤素原子电负性大小的影响：当石墨二炔表面的卤素原子数目相同时,卤素原子的电负性越大,改性后石墨二炔的价带顶的位置越深. 另外,计算结果表明石墨二炔的带隙可以通过不同卤素原子的适当混合修饰来有效调节,不同卤素原子混合修饰的石墨二炔的价带底和导带顶跨越了水的氧化还原电位. 通过热力学分析进一步证明,不同卤素原子混合修饰的石墨二炔比单一卤素修饰的石墨二炔表现出更好的光催化水全解反应活性. 这项工作对于如何设计更高效的全解水光催化剂提供了洞见.     

1HNMR测定含氢硅油含氢量及分子量

以高含氢硅油、八甲基环四硅氧烷和六甲基二硅氧烷为原料,在浓硫酸催化作用下通过调聚反应制备了一系列不同规格的低含氢硅油。并通过1H NMR（以二氧六环为内标物,以氘代氯仿为溶剂）表征了该含氢硅油,由特征峰的面积比计算出了其含氢量,并与化学方法测定的含氢量进行了对比,结果表明两者间相对偏差均小于±1.9%。同时,此方法还可以求得含氢硅油链段中不同结构的链段比,从而求得含氢硅油的分子量;结合特性粘度的测定,求得含氢硅油的K值为4.21×10-5L/g,α值为0.83。K,α值不受含氢量的影响,且与文献中的值一致,表明用1H NMR测定含氢硅油分子量是可行的。该方法具有操作简单、省时、准确、可靠、所需样品量少等优点。     

Fullerene-like Si60C60 nanocage: Hydrogen storage capacity

For investigating the hydrogen storage capacity of the Si₆₀C₆₀ nanocage, we have performed first principle density functional theory calculations with van der waals corrections. According to the force and energy minimization of the complex structures of nH₂@Si₆₀C₆₀, we have found that the systems with n = 1 to 70 are energetically favorable. We also found that the most stable nH₂@Si₆₀C₆₀ system is related to the systems with n close to 50 which make it possible to reach 4.2 wt% of hydrogen storage. Although it is found that the nH₂@Si₆₀C₆₀ system remains stable up to n = 70 and 5.8 wt%. The NPT molecular dynamic investigation at different pressures (0–30 atm) and also different temperatures (300–1800 K) were carried out on the optimized stable system with maximum capacity of encapsulating H₂ molecules (70H₂@Si₆₀C₆₀).     

真空变压吸附氢气纯化的参数研究

本文首先建立了多孔介质传热传质与吸附模型,模拟了多组分气(N2:CO:CO2:CH4:H2=0.007:0.012:0.23:0.021:0.73和N2:CO:CO2:CH4:H2=0.007:0.012:0.17:0.021:0.79)在AC5-KS活性炭吸附床中的穿透曲线和真空变压吸附循环。将实验数据与模拟值进行对比验证后,分析了压力、进气流率对穿透曲线的影响,并研究了压力、进气流率、循环步数、循环操作时间条件对真空变压吸附氢气纯化的影响。结果发现,增大吸附压力,减小进气流率,减少循环步数和吸附时间,增加冲洗和升压时间都会导致产品氢气纯度上升,氢气产率和回收率下降,并且在一般情况下氢气的纯度变化趋势与氢气产率和回收率变化趋势相反。     

Chemisorption of atomic hydrogen in graphite and carbon nanotubes

An orthogonal tight-binding model of the carbon-hydrogen interaction was modified to deal with the different hybridization states of atomic hydrogen on carbon surfaces, without explicitly including charge self-consistency. The resulting model has great flexibility and computational efficiency, generally with a good quantitative accuracy. The non-self-consistent C-H model was tested by calculating structural properties of small hydrocarbons and simple polymers, and against ab initio results of H binding to both perfect and defective graphite. The model was employed to study the chemisorption properties and dynamics of atomic hydrogen on perfect and defective surfaces of graphite and carbon nanotubes.     

Energy exchange between discrete breathers in graphane in thermal equilibrium

Graphane is a fully hydrogenated graphene which is practically interesting for application in electronics, hydrogen storage and transportation, in nanoscale devices. As it was previously shown, the energy of a discrete breather (nonlinear localized mode) in graphane close to the value of the energy barrier at which the dehydrogenation of graphene occurs. In the present work, molecular dynamics simulation is used to investigate the possibility of energy exchange between discrete breathers in graphane in thermal equilibrium at 400 K and 600 K. In thermally equilibrated graphane, hydrogen atoms are spontaneously excited and can be considered as discrete breathers. Comparison of the kinetic energy per atom as the function of time for the selected hydrogen atoms with their displacements along the z axis showed that there is an energy exchange between the discrete breathers at evaluated temperatures. Hydrogen atom, transmitting its energy to the neighboring atom no longer exists as discrete breather. At high temperatures (600 K) the energy exchange between closely located discrete breathers also take place but strong thermo-oscillations of atoms at high temperatures (above 400 K) considerably affect the process.     

Density functional and dynamics study of the dissociative adsorption of hydrogen on Mg (0 0 0 1) surface

A first principles study is performed to investigate the adsorption characteristics of hydrogen on magnesium surface. Substitutional and on-surface adsorption energies are calculated for Mg (0 0 0 1) surface alloyed with the selected elements. To further analyze the hydrogen-magnesium interaction, first principles molecular dynamics method is used which simulates the behavior of H₂ at the surface. Also, charge density differences of substitutionally doped surface configurations were illustrated. Accordingly, Mo and Ni are among the elements yielding lower adsorption energies, which are found to be −9.2626 and −5.2995 eV for substitutionally alloyed surfaces, respectively. In light of the dynamic calculations, Co as an alloying element is found to have a splitting effect on H₂ in 50 fs, where the first hydrogen atom is taken inside the Mg substrate right after the decomposition and the other after 1300 fs. An interesting remark is that, elements which acquire higher chances of adsorption are also seen to be competent at dissociating the hydrogen molecule. Furthermore, charge density distributions support the results of molecular dynamics simulations, by verifying the distinguished effects of most of the 3d and 4d transition metals.     

基于反应力场的分子动力学方法研究氢在钯表面的分解

基于二阶矩近似反应力场方法构建的全维度势能面研究了氢分子及其同位素分子在钯表面的分解过程.在构建势能面的过程中数据库中只包含了氢分子与钯（111）表面相互作用的相关信息,该势能面在研究氢分子在钯（100）表面上的分解过程中表现出了非常好的可转移性.结果表明,氢分子及其同位素分子在钯（111）与钯（100）表面上的分解系数S₀均随着入射能量的增加呈现非单调变化,并且通过固定分子取向的方法发现同核分子（H₂、D₂和T₂）最有利分解取向角为90°,而异核分子（HD、HT和DT）受质心偏移的影响,其最有利分解取向角向大角度偏移.     

Study of reduction processes over cerium oxide surfaces with atomic hydrogen using ultra accelerated quantum chemical molecular dynamics

Ceria plays an important role in catalysis, due to its ability to store and release oxygen depending on the condition present in the catalyst environment. To analyze the role of ceria in catalytic reactions, it is necessary to know the details of the interaction of ceria surface with environmentally sensitive molecules. This study was conducted using ultra accelerated quantum chemical molecular dynamics. Its purpose was to investigate the reduction process of the (1 1 1) and (1 1 0) surfaces of ceria with atomic hydrogen as well as water desorption mechanisms from the surfaces. This simulation demonstrated that when a high-energy colliding hydrogen atoms are adsorbed on the ceria, it pulls up an O atom from the ceria surfaces and results in the formation of a H₂O molecule. This is the first dynamics simulation related to such reduction processes based on quantum chemistry.