Diffusion of Li ion on graphene: A DFT study

Density functional theory investigations show that the Li⁺ ion is stabilized at the center of hexagonal carbon ring with the distance of 1.84 Å from graphene surface. The potential barrier of Li⁺ ion diffusion on the graphene surface, about 0.32 eV, is much lower than that of Li⁺ ion penetrating the carbon ring which is 10.68 eV. When a vacancy of graphene exists, potential barrier about 10.25 eV for Li⁺ ion penetrating the defect is still high, and the ability of the vacancy to sizing the Li⁺ ion is also observed. Electronic densities of states show that the formation of a localized bond between Li atom and edge carbon of vacancy is the main reason for high potential barrier when Li⁺ ion penetrate a vacancy. While Coulomb repulsion is the control factor for high potential barrier in case of Li⁺ ion penetrating a carbon ring.     

Adsorption of H2S at Stone–Wales defects of graphene-like BC3: a computational study

We employed density functional theory to characterise H₂S adsorption, and dissociation on the pristine and Stone–Wales (SW) defected BC₃ graphenes. H₂S is predicted to be weakly adsorbed on the pristine graphene with the adsorption energy of about 7.11 kcal/mol. Two types of SW defects were generated by rotating a C–C bond (SW-CC) or a B–C bond (SW-BC) by about 90°. We predict that, in contrast to SW-BC, dehydrogenation of H₂S is energetically more favourable on the SW-CC compared to the associative adsorption. It is also found that SW-CC formation is more favourable than the formation of SW-BC. Molecular adsorption of H₂S on both of the SW defected sheets is more favourable than that on the pristine sheet. The preferable adsorption process on the SW-BC and SW-CC defected graphene sheets is via associative and dissociative mechanisms, respectively. Furthermore, the highest occupied molecular orbital and lowest unoccupied molecular orbital energy gap of the SW-BC defected sheet is highly sensitive to the adsorption process which may be used for the detection of H₂S.     

Geometric stability and adsorption property of hydroxyl group on graphene sheets

The stable geometrics and adsorption behaviors of hydroxyl (OH) groups on graphene sheets are investigated using the first-principles calculations. The single hydroxyl adatom has small adsorption energy and diffusion barrier on pristine graphene. The binding strength of the hydroxyl group increases with the coverage, and the aggregations of the hydroxyl groups reduce the structural bucking of graphene sheet. On the graphene with single vacancy (SV-graphene), the large trapping zones mean the adsorbed OH would be easily trapped at the vacancy site. The hydroxyl groups prefer to aggregate on graphene surfaces and form the water molecule, leaving the epoxy group on pristine graphene or oxygen dopant in SV-graphene, which is used to constitute the structural model of oxidized graphene. These results would provide us a useful reference to understand the atomic structure and adsorption property of functional groups on graphene sheets.     

Ionic conductivity of pure and doped Li3N

The ionic conductivity of Li₃N crystals doped with various metal ions (magnesium, copper and aluminum) or hydrogen has been investigated. The metal ions have a negative effect on the conductivity whereas hydrogen increases it. The intrinsic Li⁺ ionic conductivity of pure Li₃N is (2·-4)×10^-4Ω^-1cm^-1 at room temperature with an activation energy of 0.26?0.27 eV. Doping with hydrogen to a maximum level of 0.5?1.0 atom% results in a conductivity of 6×10^-3Ω^-1cm^-1 and an activation energy which has been lowered to 0.20 eV. A model is proposed for the action of hydrogen whereby the Li-N bonds next to an NH^2- group are weakened thereby facilatating the creation of Li⁺ Frenkel defects and the vacancy migration. Hydrogen-doped Li₃N is termed an enhanced intrinsic conductor.     

Metal-decorated defective BN nanosheets as hydrogen storage materials

Density functional theory computations were performed to investigate hydrogen adsorption in metaldecorated defective BN nanosheets. The binding energies of Ca and Sc on pristine BN nanosheets are much lower than the corresponding cohesive energies of the bulk metals; however, B vacancies in BN nanosheets enhance the binding of Ca and Sc atoms dramatically and avoid the clustering of the metal atoms on the surface of BN nanosheets. Ca and Sc strongly bind to defective BN nanosheets due to charge transfer between metal atoms and BN nanosheets. Sc-decorated BN nanosheets with B vacancies demonstrate promising hydrogen adsorption performances with a hydrogen adsorption energy of ?0.19～ ?0.35 eV/H₂.     

A DFT study of formaldehyde adsorption on functionalized graphene nanoribbons

Density functional theory (DFT) based ab initio calculations were done to monitor the formaldehyde (CHOH) adsorptive behavior on pristine and Ni-decorated graphene sheet. Structural optimization indicates that the formaldehyde molecule is physisorbed on the pristine sheet via partly weak van der Waals attraction having the adsorption energy of about −15.7 kcal/mol. Metal decorated sheet is able to interact with the CHOH molecule, so that single Ni atoms prefer to bind strongly at the bridge site of graphene and each metal atom bound on sheet may adsorb up to four CHOH. The findings also show that the Ni decoration on graphene surface results in some changes in electronic properties of the sheet and its E_g is remained unchanged after adsorption of CHOH molecules. It is noteworthy to say that no bond cleavage was observed for the adsorption of CHOH on Ni-decorated graphene.     

钠在空位石墨烯上吸附性能的研究

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯和空位石墨烯吸附钠原子的电荷密度、吸附能、态密度和储存量.结果表明,在两种石墨烯中,钠原子的最佳吸附位置都为H位.空位石墨烯对钠原子的吸附能是-2. 46 eV,约为本征石墨烯对钠原子吸附能的3. 4倍;钠原子与空位石墨烯中的碳原子发生轨道杂化,而与本征石墨烯没发生轨道杂化现象.存在一个空位的石墨烯能够吸附5个钠原子,与本征石墨烯相比显著提高.因此,空位石墨烯有望成为一种潜在的储钠材料.     

Na在B掺杂的空位石墨烯上吸附性能的第一性原理研究

采用基于密度泛函理论的第一性原理方法,研究了本征石墨烯和B掺杂的空位石墨烯吸附Na原子的电荷密度、吸附能、态密度、储存量以及电极电压.结果表明,两种石墨烯中,Na原子的最佳吸附位置都是H位.B掺杂的空位石墨烯对Na原子的吸附能是-2.08 eV,比本征石墨烯对Na原子的吸附能(-0.71eV)低很多.B掺杂的空位石墨烯中Na原子与B原子发生轨道杂化,本征石墨烯中没有杂化现象.B掺杂的空位石墨烯能够吸附12个Na原子,较本征石墨烯多.因此,B掺杂的空位石墨烯更适合储钠.     

Hofmeister series and ionic effects of alkali metal ions on DNA conformation transition in normal and less polarised water solvent

Normal and less polarised water models are used as the solvent to investigate Hofmeister effects and alkali metal ionic effects on dodecamer d(CGCGAATTCGCG) B-DNA with atomic dynamics simulations. As normal water solvent is replaced by less polarised water, the Hofmeister series of alkali metal ions is changed from Li⁺ > Na⁺ ? K⁺ ? Cs⁺ ? Rb⁺ to Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺. In less polarised water, DNA experiences the B→A conformational transition for the lighter alkali metal counterions (Li⁺, Na⁺ and K⁺). However, it keeps B form for the heavier ions (Rb⁺ and Cs⁺). We find that the underlying cause of the conformation transition for these alkali metal ions except K⁺ is the competition between water molecules and counterions coupling to the free oxygen atoms of the phosphate groups. For K⁺ ions, the ‘economics’ of phosphate hydration and ‘spine of hydration’ are both concerned with the DNA helixes changing.     

Methane molecule over the defected and rippled graphene sheet

Adsorption of a methane molecule (CH₄) onto a defected and rippled graphene sheet is studied using ab initio and molecular mechanics calculations. The optimal adsorption position and orientation of this molecule on the graphene surface (motivated by the recent realization of graphene sensors to detect individual gas molecules) is determined and the adsorption energies are calculated. In light of the density of states, we used the SIESTA code. It is found that (i) classical force field yields adsorption energy comparable with experimental result and ab initio calculation; (ii) the periodic nature of the van der Waals potential energy stored between methane and perfect sheet is altered due to the insertion vacancies and sinusoidal ripples; (iii) the van der Waals potential energy is found to be sensitive to the presence of the vacancies and the ripples so that the added molecule avoids to be around vacant cites and on top of the peaks.     

Formation of oxygen vacancies on the TiO2(1 1 0) surfaces

Density functional theory was employed to investigate the formation and properties of the oxygen vacancies on the rutile TiO₂(1 1 0) surface. It is found that the formation of the positively charged bridging-oxygen vacancy (BOV⁺, 4.2 eV) is the most favored one, followed by the positively charged in-plane-oxygen vacancy (POV⁺, 4.5 eV). In contrast, the formation of the neutral bridging-oxygen and in-plane-oxygen vacancies (BOV and POV), and their dication oxygen vacancies (BOV²⁺ and POV²⁺) needs much higher energies (7.9 and 8.3 vs. 8.1 and 8.6 eV), respectively.     

掺杂石墨烯吸附特性的第一性原理研究

利用第一性原理方法研究了一氧化碳分子在本征和硼、氮、铝、磷掺杂的有限尺寸石墨烯上的吸附机理.结果表明,石墨烯作为一氧化碳传感器时的性能依赖于掺杂元素.本征、硼和氮掺杂石墨烯吸附一氧化碳时的吸附能较低,为物理吸附.铝、磷掺杂石墨烯的吸附能显著提高,比本征、硼和氮掺杂时高出约一个数量级,且铝和磷原子从石墨烯中突出,使其发生局部弯曲.铝掺杂石墨烯增强了石墨烯与一氧化碳分子之间的相互作用,可以提高石墨烯的气敏性和吸附能力,是一氧化碳传感器的最佳候选材料之一.     

Y掺杂空位石墨烯对NO及CO气体表面吸附的第一性原理研究

摘　要：基于第一性原理的计算方法,建立了本征石墨烯、空位石墨烯及钇( Y)掺杂空位石墨烯模型,并计算了CO、NO在三类石墨烯表面的吸附过程. 从表面能、吸附结构、吸附能和态密度四个方面进行分析讨论,研究掺杂Y对CO、NO气体吸附性能的影响. 结果表明：CO、NO与本征石墨烯之间的吸附为弱的物理吸附,掺杂Y后增强了材料表面对CO、NO的吸附效果,最大吸附能分别为7.414eV、6.702eV,属于化学吸附;掺杂Y使空位石墨烯费米能级附近有了更多的活跃电子,其吸附NO后体系由半金属转变为金属特性,该特性能为开发更加优良的石墨烯气敏材料提供理论支持.     

Colorimetric quantitative sensing of alkali metal ions based on reversible assembly and disassembly of gold nanoparticles

A novel and simple method for the colorimetric quantitative sensing of individual alkali metal ions (Li⁺, Na⁺, K⁺, and Rb⁺) based on the reversible properties of self-assembled aggregates and individual gold nanoparticles (Au NPs) is described. This paper demonstrates reversible self-assembly processes where the degree of assembly and disassembly is dependent on the individual alkali metal ion concentration, nanoparticle size, and alkali metal ionic radii. The color changes of the colloidal Au NPs with metal ion concentrations in colloidal NP solutions occur reversibly. Below a certain concentration of alkali metal ions, the aggregates of Au NPs are redispersed. As the Au NP diameters and the alkali metal ionic radii increase, the critical concentration decreases.     

Vibration analysis of defected and pristine triangular single-layer graphene nanosheets

This paper investigates the vibration behavior of pristine and defected triangular graphene sheets; which has recently attracted the attention of researchers and compare these two types in natural frequencies and sensitivity. Here, the molecular dynamics method has been employed to establish a virtual laboratory for this purpose. After measuring the different parameters obtained by the molecular dynamics approach, these data have been analyzed by using the frequency domain decomposition (FDD) method, and the dominant frequencies and mode shapes of the system have been extracted. By analyzing the vibration behaviors of pristine triangular graphene sheets in four cases (right angle of 45-90-45 configuration, right angle of 60-90-30 configuration, equilateral triangle and isosceles triangle), it has been demonstrated that the natural frequencies of these sheets are higher than the natural frequency of a square sheet, with the same number of atoms, by a minimum of 7.6% and maximum of 26.6%. Therefore, for increasing the resonance range of sensors based on 2D materials, non-rectangular structures, and especially the triangular structure, can be considered as viable candidates. Although the pristine and defective equilateral triangular sheets have the highest values of resonance, the sensitivity of defective (45,90,45) triangular sheet is more than other configurations and then, defective (45,90,45) sheet is the worst choice for sensor applications.     

Cation-mediated sandwich formation between benzene and pillar[5]arene: a DFT study

Cation–π interactions in alkali metal ion (Li⁺, Na⁺ and K⁺)–pillar[5]arene complexes and sandwiches of pillar[5]arene and benzene formed via alkali metal ions are studied in the light of density functional theory. Several possible modes of interaction between metal ions and pillar[5]arene have been studied. Results suggest that interaction is stronger in the complexes with the metal ion present inside the cavity of the pillar[5]arene as compared to that where the metal ion is outside the cavity. The calculated interaction energy further reveals that though cation–π complexes with larger number of alkali metal ions are unstable, however, corresponding sandwiches are stable, which further support the fact that pillar[5]arene–metal ion complexes can interact with other π–electron-rich species. Absorption spectra of the complexes formed undergo both blue and red shifts as compared to the pillar[5]arene.     

非金属与金属原子共掺杂石墨烯体系的气敏特性研究

采用基于密度泛函理论的第一性原理方法研究了非金属N原子和金属原子(M=Mo,Al,Co,Fe,Au和Pt)共掺杂石墨烯体系(M-GN4)的电子结构和表面活性.研究发现:单个金属原子掺杂的GN4体系表现出不同的稳定性,相比掺杂的Au原子,其它的金属原子都具有很高的稳定性( 6. 0 e V).掺杂的金属原子失去电荷显正电性将有助于调控气体分子的吸附特性. Mo-GN4和Al-GN4衬底对吸附的O_2表现出较高的灵敏性,单个CO和O_2分子在Co-GN4和Fe-GN4衬底的吸附能差别较小.此外,吸附不同的气体分子能够有效地调控M-GN4体系的电子结构和磁性变化.     

First-principles study of lithium intercalated bilayer graphene

Lithium intercalated bilayer graphene has been investigated using first-principles density functional theory calculations. Results show that there exist AB and AA stacking sequences for bilayer graphene in which the latter is more favorable for the Li storage and the former will evolve into the latter with the intercalation of Li ions. The relationship between the interlayer distance of two graphene sheets and the intercalated capacity of Li ions is discussed. It is found that structural defect is identified to store Li ions more favorably than pristine bilayer graphene and an isolated C atom vacancy in bilayer graphene can capture three Li ions between two graphene sheets.     

N-doped graphene as a nanostructure adsorbent for carbon monoxide: DFT calculations

ABSTRACT

This work reports the physisorption of carbon monoxide (CO) on the surface of N-doped graphene. To study the adsorption of CO on N-doped graphene, some quantum chemical calculations were used through density functional theory. Based on our results, it can be found that the CO molecule could be adsorbed on the surface of N-doped graphene physically with the adsorption energies (E_ads) of ?2.9 and ?0.8 kcal mol^?1 (depends on the kind of configuration) while positive adsorption energies were calculated upon adsorption of CO on pristine graphene. We used the charge analysis for calculation of the net transferred charge of adsorbed CO on pristine and N-doped graphene sheets to evaluate the sensing ability of surface. The global indices of reactivity were calculated from the differences of the lowest unoccupied molecular orbital and highest occupied molecular orbital energies. Graphs for density of states point to some orbital hybridisation between CO molecule and N-doped graphene. Consequently, the N-doped graphene transforms the existence of CO molecules into electrical signal, and it may be potentially used as a sensor for CO.     

Measurement of the sputter yield after mild ion erosion of a pristine Cu(001) surface

Using the STM technique we have determined the sputter yield on a pristine Cu(001) surface after mild (fluence less than 0.044 ions per surface atom) bombardment of the pristine surface with 800 eV Ar⁺ions at normal incidence. The experiments have been performed at substrate temperatures ranging from 200 to 350 K. Making use of the positional correlation of adatoms and surface vacancies, at 200 K and 325 K, we concluded that about 1/3 of the surface adatoms originate from interstitials arriving at the surface and they give a direct indication of the buried bulk vacancies. A careful analysis of the different areas for surface vacancies and adatom then allowed a quantitative evaluation of the sputter yield at 1.2 Cu atoms per 800 eV Ar⁺ ion.