Au_7团簇吸附O_2和CO及其对CO的催化反应机理研究

本文采用密度泛函理论,研究了Au_7团簇催化CO的氧化反应机理.研究发现,二维平面结构的Au_7团簇更容易吸附CO和O_2分子. Au_7团簇吸附一个O_2分子的吸附能为0.64 eV,但在吸附多个O_2分子时,平均吸附能有了明显的下降,表明Au_7团簇进行多吸附O_2分子的可能性不大. Au_7团簇吸附一个CO分子的吸附能为1.26 eV,且在吸附多个CO分子时,平均吸附能虽有减少,但减小的幅度不大,说明Au_7团簇有可能吸附多个CO分子.此外,在Au_7团簇催化CO的氧化反应过程中,整个反应克服的最高势垒仅为0.34 eV,说明Au_7团簇有望成为良好的CO氧化催化剂.     

Theoretical study of hydrogen adsorption in Ti-decorated capped carbon nanotube

We present ab initio study using dispersion-corrected density functional theory calculations to investigate the hydrogen interaction with Ti-coated, one end closed, single-walled carbon nanotube (SWCNT). Our results demonstrate that a single Ti atom binds up to five hydrogen molecules on SWCNT cap top, whereas adsorption of four hydrogen molecules is energetically more favourable. The analyses from adsorption energy profile, highest occupied molecular orbital–lowest unoccupied molecular orbital gap and Mulliken charge distribution show contrast in first hydrogen molecule adsorption compared with the rest of four configurations. This is clearly due to the strongly different bonding nature of first hydrogen adsorption among others, between hydrogen molecules and Ti-coated SWCNT. These results not only support our understanding of adsorption nature of hydrogen in Ti-coated SWCNTs but also suggest new directions for smart storage techniques.     

Diffusion of CO2/CH4 confined in narrow carbon nanotube bundles

ABSTRACT

The diffusion of a CO₂/CH₄ mixture in carbon nanotube (CNT) bundles was studied using molecular simulations. The effect of diameter and temperature on the diffusion of the mixture was investigated. Our results show that the single-file diffusion occurs when CO₂ and CH₄ are confined in CNTs of diameter less than 1.0 nm. In CNTs of diameter larger than 1.0 nm, both molecules diffuse in the Fickian style. The transition from single-file to Fickian diffusion was demonstrated for both CO₂ and CH₄ molecules. A dual diffusion mechanism was observed in the studied (20, 0) CNT bundle, single-file diffusion of CO₂ in the interstitial sites of (20, 0) CNT bundle and Fickian diffusion of CO₂ and CH₄ in the pores. For CO₂, the interaction energies (CO₂–CO₂ and CO₂–CNT) are larger than that of CH₄ in all cases. But only a very small difference in the diffusion coefficient was observed between CO₂ and CH₄. Temperature has a negligible effect on the difference between diffusion coefficients of CO₂ and CH₄ in the studied CNT bundles. The adsorption, diffusion and permeation selectivities are discussed and compared, and the adsorption is demonstrated to be the rate limiting step for the separation of CO₂/CH₄ in CNT bundle membranes.     

密度泛函理论研究CO与Nin（n=1—6）团簇的相互作用

采用密度泛函理论对CO吸附在镍团簇表面进行了系统研究.结果表明,Ni_nCO团簇的最低能量结构是在Ni_n团簇最低能量结构的基础上吸附CO生长而成,CO的吸附没有改变Ni_n团簇的结构;CO分子在Ni_n团簇表面发生的是非解离性吸附,与优化的CO键长（0.1138?nm）相比,吸附后C—O键长变长（0.1180—0.1214?nm）,表明吸附后C—O键被削弱,CO分子被活化.自然键轨道分析表明,CO分子只与最近邻的Ni原子发生相互作用;CO分子与Ni原子相互作用的本质是CO分子内的杂化轨道与Ni原子3d, 4s, 4p轨道相互作用的结果. 关键词： nCO团簇')" href="#">Ni_nCO团簇 n团簇')" href="#">Ni_n团簇 平衡结构 电子性质     

Sc_(13)团簇的稳定性和磁性研究

使用梯度修正的密度泛函理论,对Sc_(13)团簇的稳定性和磁性进行了广泛的研究.与邻近钪团簇,或者与其它13-原子3d过渡金属团簇相比,Sc_(13)团簇的基态结构二十面体具有最高对称性,结构和磁性均表现出高的稳定性.由于二十面体的高对称性,Sc_(13)团簇的对称性分子轨道为晶体场分裂壳层9A_g(1),10T_(1u)(3),8H_g(5),10A_g(1),6T_(2u)(3),11T_(1u)(3),3G_g(4),3G_u(4),and 9H_g(5).20个价电子以类似于凝胶模型的1S~21P~61D~(10)2S~2壳层填充前四组壳层,其余19个价电子依据洪德法则填充后五组壳层,从而产生了19.0μB的磁矩.5个半填充的晶体场分裂壳层与离域价电子填充的1S~21P~61D~(10)2S~2类壳层导致了稳定的高磁矩Sc_(13)团簇.     

有限长扶手椅形单壁碳纳米管分子静电势的理论研究

在混合密度泛函B3LYP理论下,用3-21G基函数对有限长扶手椅形单壁碳纳米管(4,4)、(5,5)和(6,6)的构型进行优化和分子静电势计算.结果表明:除近核区域为正常的正电势外,碳纳米管结构模型的管内和管外为负电势区域;在碳纳米管结构模型的管内,管心处均出现负电势的最小值,且负电势的绝对值随着碳纳米管的曲率降低而增大,管心轴线上静电势的变化随碳纳米管的曲率降低而减少,带电粒子流比较容易通过纳米管.     

[C2MIM]+在碳纳米管中结构和性质的理论研究

采用密度泛函理论方法,系统研究了1-乙基-3-甲基咪唑离子 ( [C2MIM]+ ) 在三种不同管径的碳纳米管中的稳定结构、相互作用能和分子轨道性质. 研究表明,随着碳纳米管管径的增加,[C2MIM]+在碳纳米管内的稳定结构从居中的位置越发靠近碳纳米管的管壁,其与碳纳米管的结合能也从-45.52 kcal/mol降低到-39.45 kcal/mol. 通过分析[C2MIM]+在不同尺寸碳纳米管中的分子轨道排布,发现研究体系的HOMO轨道和LUMO轨道主要是局域在碳纳米管上,电子跃迁表现为π→π*,表明[C2MIM]+与碳纳米管之间为弱的范德华作用. 本研究为理解离子液体与碳纳米管之间的相互作用提供了重要的理论基础.     

Structural, curvature and electronic properties of Rh adsorption on armchair single-walled carbon nanotube

This paper systematically studies the rolling effects of the (n, n) single-wall carbon nanotubes (SWCNT) with different curvatures on Rh adsorption behaviours by using density functional theory. The outside charge densities of SWCNTs are found to be higher than those inside, and the differences decrease with the increase of the tube radius. This electronic property led to the discovery that the outside adsorption energies are higher than the inside ones, and that the differences are reduced with the increase of the tube radius. Partial density of states and charge density difference indicate that these strong interactions induce electron transfer between Rh atoms and SWCNTs.     

CO oxidation over BC3 nanosheet: a theoretical study

ABSTRACT

Metal-free catalysts have attracted more attention due to their highly active in catalytic oxidation reactions. The electronic structure and catalytic property of BC₃ sheet are investigated by using first-principles calculations. It is found that the BC₃ sheet as the active surface can effectively regulate the adsorptive stability of reactive gases. Besides, the possible reaction processes for CO oxidation on the BC₃ sheet are comparably analysed through different reaction mechanisms, which include the Eley–Rideal (ER), Langmuir–Hinshelwood (LH) and termolecular Eley–Rideal (TER). In the CO oxidation reactions, the decomposition of O₂ molecule as the starting state (0.40?eV) is an energetically more favourable process than those of other processes, the Eley–Rideal (ER) reactions (2O_ads+2CO→CO₂) are more prone to take place with lower energy barriers (3 sheet. These results provide an important guidance on exploring the highly efficiency metal-free catalyst for CO oxidation.     

氮掺杂及水分子吸附碳纳米管电子场发射第一性原理研究

对闭口碳纳米管(CNT)顶端分层掺氮及吸附不同数目水分子体系,运用第一性原理研究了有电场存在时的电子场发射性能.结果表明：掺氮并吸附水分子的CNT结构稳定;外电场愈强、水分子数愈多,体系态密度(DOS)向低能端移动幅度愈大且最高分子占据轨道(HOMO)/最低分子空轨道(LUMO)能隙愈小.吸附能,DOS/LDOS,HOMO/LUMO及其能隙分析一致表明,第三层氮掺杂CNT吸附不同数目水分子体系的场发射性能最佳. 关键词： 氮掺杂 水吸附 密度泛函理论 电子场发射     

掺硼水吸附碳纳米管电子场发射性能的第一性原理研究

运用第一性原理研究了掺硼碳纳米管(BCNT)顶端吸附水分子后的电子场发射性能.结果表明：掺B及吸附H₂O的碳纳米管(BCNT+H₂O)端部形成电子聚集的原子尺度微区,其电子态密度(DOS)在费米能级(E_f)附近有很大提高.根据计算的电子DOS,HOMO/LUMO及Mulliken电荷分布等可知BCNT+H₂O比CNT+H₂O有更好的场发射性能. 关键词： 掺硼碳纳米管 吸附 密度泛函理论 电子场发射     

Electrical transport properties of CaMnO3 thermoelectric compound: a theoretical study

The electrical transport coefficients of anti-ferromagnetic CaMnO₃ have been investigated by density functional theory calculation within generalized gradient approximation. The calculated transport coefficients exhibit the anisotropic nature, in agreement with its electronic states. The transport property results reveal the stronger carrier transport along the O1–Mn–O1 plane within the O–Mn–O octahedron, indicating that the Mnd and O1p orbitals are mainly responsible for electrical transport. The maximum power factor values as a function of relaxation time reach 8.4×10²³ Wm⁻¹ K⁻² s⁻¹, 7.9×10²³Wm⁻¹ K⁻² s⁻¹ and 4.9×10²³ Wm⁻¹ K⁻² s⁻¹ within c, a and b direction, respectively. The dimensionless figure of merit ZTxx, ZTyy as well as ZTzz is estimated with 1.28, 0.8 and 1.37 at 1000 K, respectively.     

Field emission properties of capped carbon nanotubes doped by alkali metals:a theoretical investigation

The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation.The results indicate that the adsorption of alkali metal on the center site of a CNT tip is energetically favorable.In addition,the adsorption energies increase with the introduction of the electric field.The excessive negative charges on CNT tips make electron emittance much easier and result in a decrease in work function.Furthermore,the inducing effect by positively charged alkali metal atoms can be reasonably considered as the dominant reason for the improvement in field emission properties.     

Infrared spectra and stability of CO and H2O sorption over Ag-exchanged ZSM-5 zeolite: DFT study

The infrared spectra and stability of CO and H₂O sorption over Ag-exchanged ZSM-5 zeolite were investigated by using density function theory (DFT). The changes of NBO charge show that the electron transfers from CO molecule to the Ag⁺ cation to form an σ-bond, and it accompanies by the back donation of d-electrons from Ag⁺ cation to the CO (π*) orbital as one and two CO molecules are adsorbed on Ag-ZSM-5. The free energy changes ΔG, −5.55 kcal/mol and 6.52 kcal/mol for one and two CO molecules, illustrate that the Ag⁺(CO)₂ complex is unstable at the room temperature. The vibration frequency of C-O stretching of one CO molecule bonded to Ag⁺ ion at 2211 cm⁻¹ is in good agreement with the experimental results. The calculated C-O symmetric and antisymmetric stretching frequencies in the Ag⁺(CO)₂ complex shift to 2231 cm⁻¹ and 2205 cm⁻¹ when the second CO molecule is adsorbed. The calculated C-O stretching frequency in CO-Ag-ZSM-5-H₂O complex shifts to 2199 cm⁻¹, the symmetric and antisymmetric O-H stretching frequencies are 3390 cm⁻¹ and 3869 cm⁻¹, respectively. The Gibbs free energy change (ΔGH₂O) is −6.58 kcal/mol as a H₂O molecule is adsorbed on CO-Ag-ZSM-5 complex at 298 K. The results show that CO-Ag-ZSM-5-H₂O complex is more stable at room temperature.     

MgO-decorated carbon nanotubes for CO2 adsorption: first principles calculations

The global greenhouse effect makes it urgent to deal with the increasing greenhouse gases.In this paper the performance of MgO-decorated carbon nanotubes for CO 2 adsorption is investigated through first principles calculations.The results show that the MgO-decorated carbon nanotubes can adsorb CO 2 well and are relatively insensitive to O 2 and N 2 at the same time.The binding energy arrives at 1.18 eV for the single-MgO-decorated carbon nanotube adsorbing one CO 2 molecule,while the corresponding values for O 2 and N 2 are 0.55 eV and 0.06 eV,respectively.In addition,multi-molecule adsorption is also proved to be very satisfactory.These results indicate that MgO-decorated carbon nanotubes have great potential applications in industrial and environmental processes.     

Spin polarization effect of Ni2 molecule

The density functional theory （DFT） method （b3p86） of Gaussian 03 is used to optimize the structure of the Ni2 molecule. The result shows that the ground state for the Ni2 molecule is a 5-multiple state, symbolizing a spin polarization effect existing in the Ni2 molecule, a transition metal molecule, but no spin pollution is found because the wavefunction of the ground state does not mingle with wavefunctions of higher-energy states. So the ground state for Ni2 molecule, which is a 5-multiple state, is indicative of spin polarization effect of the Ni2 molecule, that is, there exist 4 parallel spin electrons in Ni2 molecule. The number of non-conjugated electrons is greatest. These electrons occupy different spatial orbitals so that the energy of the Ni2 molecule is minimized. It can be concluded that the effect of parallel spin in the Ni2 molecule is larger than that of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell-Sorbie potential functions with the parameters of the ground state and other states of the Ni2 molecule are derived. The dissociation energy De for the ground state of the Ni2 molecule is 1.835 eV, equilibrium bond length Re is 0.2243 nm, vibration frequency we is 262.35 cm^-1. Its force constants f2, f3 and f4 are 1.1901 aJ.nm^-2, -5.8723 aJ.nm^-3, and 21.2505 aJ.nm^-4 respectively. The other spectroscopic data for the ground state of the Ni2 molecule ωeχe, Be and αe are 1.6315cm 2, 0.1141 cm^-1, and 8.0145× 10^-4 cm^-1 respectively.     

Metal oxide nanoclusters as drug delivery systems for an anticancer drug: a theoretical study

In this study, the reactivity and electronic sensitivity of the Be₁₂O₁₂, Mg₁₂O₁₂, and Zn₁₂O₁₂ nanoclusters were investigated for 6-thioguanine (TG) anticancer drug using density functional theory calculations at the gas phase and aqueous solution. Our results show that the electronic properties of Mg₁₂O₁₂ and Zn₁₂O₁₂ nanoclusters are significantly sensitive to the presence of TG and the nanoclusters may be a promising candidate for adsorption of this drug. The results show that all complexes are energetically favourable, especially in the aqueous phase. Also, our ultraviolet–visible results show that the electronic spectra of TG/(MO)₁₂ complexes exhibit a blue shift toward lower wavelengths (higher energies). In order to go further and gain insight into the binding features of considered (MO)₁₂ nanoclusters with TG drug, the Atoms in Molecules analysis was performed. Consequently, the results demonstrated that the Mg₁₂O₁₂ and Zn₁₂O₁₂ nanoclusters could be used as potential carriers for the delivery of TG drug.

The results represented that the Mg₁₂O₁₂ and Zn₁₂O₁₂ nanoclusters could be used as potential carriers for delivery of 6-thioguanine drug in the nanomedicine domain.     

Isomers of the Cu5 cluster: a density function theory study

In this work,a systematic study of some possible isomer structures of the Cu 5 cluster obtained from density functional theory methods is presented.The polarisation and pseudopotential basis sets are employed in the calculations.The results show that the binding energies,frequencies,coordination numbers and average bond lengths are in reasonable agreement with reported experimental data.Moreover,four isomers of the Cu 5 cluster are obtained according to calculations,in which the most stable configuration is the planar structure.Meanwhile,two three-dimensional structures of the Cu 5 cluster are obtained in this work,which might be valuable for further theoretical and experimental studies.In addition,our study proves the possibility of the isomer structures of the Cu 5 cluster.     

Theoretical investigation of CO adsorption on TM-doped (MgO)12 (TM = Ni, Pd, Pt) nanotubes

CO adsorption on TM-doped magnesia nanotubes (TM = Ni, Pd and Pt) have been studied by using density functional theory. Our calculation results show that CO favors adsorption on TM-doped magnesia nanotubes in the form of C atom bonding with TM atom. Fukui indices analysis clearly exhibits that doping of impurity TM atom allows for a noticeably enhancement of nucleophilic reactivity ability of magnesia nanotube. The adsorption energies demonstrate that CO molecule is more strongly bound on the 3-fold TM atoms than the 4-fold TM atoms. This finding is well confirmed by TM-C bond length, charge transfer and C-O vibrational frequency. The high adsorption energy of 2.55 eV is found when CO adsorbs on 3-fold Pt in Pt-doped magnesia nanotubes, implying the kind of the doping TM atom has a significant influence on the chemical reactivity.     

Beryllium oxide (BeO) nanotube provides excellent surface towards adenine adsorption: A dispersion-corrected DFT study in gas and water phases

Zigzag (5, 0) BeO nanotube (BeONT) has been examined in detail towards adsorption properties of adenine nucleobase on its surface via D2-DFT calculation method in the gas and water phases. A detailed surface study reveals that there are four orientations for nucleobase adsorption that none of the vibrational spectrums demonstrated imaginary frequency, recognizing that all of the relaxed structures are at the minimum of energy. The minimum and maximum adsorption energies are both in chemisorption regime with calculated values of −140 (−118 BSSE corrected) and −191 (−168 BSSE corrected) in the gas phase, and −181 and −310 kJ/mol in the water phase, using meta-hybrid functional (ꞷB97XD) and 6-31G** basis set. For all positions, BeONT showed p-type semiconducting property because of receiving electronic charge from adenine molecule. Our findings suggest that BeONT could be used as a possible strong carrier for adenine molecule in practical applications.