CO在Pu(100)表面吸附的研究

采用密度泛函理论(DFT)研究了CO分子在Pu (100)面上的吸附. 计算结果表明：CO在Pu (100)表面的C端吸附比O端吸附更为有利，属于强化学吸附. CO吸附态的稳定性为穴位倾斜>穴位垂直>桥位>顶位. CO分子与表面Pu原子的相互作用主要源于CO分子的杂化轨道和Pu原子的杂化轨道的贡献. 穴位倾斜吸附的CO分子的离解能垒较小(0.280eV)，表明在较低温度下，CO分子在Pu (100)表面会发生离解吸附，离解的C，O原子将占据能量最低的穴位.     

Pu(100)表面吸附CO2的密度泛函研究

采用广义梯度密度泛函理论的改进Perdew-Burke-Ernzerh方法结合周期性层晶模型,研究了CO₂分子在Pu（100）面上的吸附和解离.吸附能和几何构型的计算表明,CO₂以穴位C4O4构型吸附最为有利,吸附能为1.48 eV.布居分析和态密度分析表明,CO₂与Pu表面相互作用的本质主要是CO₂分子的杂化轨道2π_μ与Pu5f,Pu6d,Pu7s轨道通过强电子转移和弱重叠杂化的方式相互作用而生成了新的化学键.计算的CO₂→CO+O解离能垒为0.66 eV,解离吸附能为2.65 eV, 表明在一定热激活条件下CO₂分子倾向于发生解离性吸附.O₂,H₂,CO和CO₂在Pu （100）面吸附的比较分析表明,较低温度下的吸附强度顺序依次为O₂,CO,CO₂,H₂;较高温度下的吸附强度顺序依次为O₂,CO₂,CO,H₂. 关键词： 密度泛函理论 Pu （100） 2')" href="#">CO₂ 吸附和解离     

低覆盖度CO分子在 Ni（110）面的吸附研究

利用密度泛函理论研究了低覆盖度下CO分子在Ni（110）表面的吸附结构和电子态。研究结果表明：在低覆盖度情况下, CO分子优先垂直吸附在短桥位，其次是顶位和长桥位。垂直短桥位吸附、顶位吸附相应的振动频率分别是1850.52 cm-1、1998.08cm-1。态密度的研究结果表明：CO分子和Ni原子在-10 eV -8 eV，-8 eV—-6 eV及1 eV -5 eV能量范围内发生了杂化作用。-10ev -8ev能量范围内的杂化主要来源于C、O原子的s轨道、pz轨道与Ni原子s、p、d轨道的杂化作用。-8ev—-6ev能量范围内的杂化作用主要来源于C、O原子的py、 px轨道与Ni原子d、s轨道的杂化作用。轨道间的杂化作用是吸附作用的主要来源。 我们计算的吸附位置与相应的振动频率与相关实验结果基本一致。     

NO在金属Be_n(n=2-12)团簇表面的平行吸附

采用密度泛函理论(DFT)中的广义梯度近似(GGA),对Be_nNO (n=2-12)团簇进行了构型优化,稳定性和电子性质分析.结果表明:从n=3开始,Be_nNO的基态均为NO分子平行吸附于主团簇Be_n某一表面时形成的,此时N-O键自然断裂(N-O键伸长量均超过了100%),而N端吸附于Be-Be桥位的结构仅是Be_nNO (n=2-12)团簇的一个亚稳态结构.成键性质分析表明,NO平行吸附时,N,O原子倾向于同时吸附于近邻的三个Be原子面位,相应的Be_n团簇表现出了很好的吸附能力.此时N, O原子的sp~3轨道杂化出现的孤对电子对N-O键的断裂产生了重要影响.     

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     

H2O在LiH固体表面的吸附与成键

用基于密度泛函理论的局域密度近似平面波超软赝势方法,计算了H2O分子在LiH表面的最佳吸附方式,得到了倾斜吸附的构型,其偏转角为37.85°.由吸附前后的态密度(DOS)图可知,成键主要由LiH的s、p轨道和H2O的sp3轨道杂化而成,成键峰重叠性较强,且峰增宽,有明显的共价成分.其吸附能为-43.2 kJ/mol,为化学吸附.结果显示,H2O分子在LiH表面吸附的吸附性质和构型与实验结果一致,并有形成LiOH的趋势.     

钚氧化物的分子结构和分子光谱研究

用杂化密度泛函(B3LYP)方法,Pu原子采用相对论有效原子实势(RECP),O原子采用全电子6-311g(d)基组优化了PuO,PuO2,Pu2O3的分子结构,得到了相应的平衡几何构型,并计算了红外振动频率(IR)、Raman光谱.结果表明:PuO,PuO2分子基态几何构型和振动频率与实验值相符.对Pu2O3分子可能的构型和多重性进行结构优化,发现Pu2O3分子基态为11B2的C2v构型,给出了Pu2O3分子基态结构的红外和拉曼光谱数据、力常数等系列数据,并对振动频率的峰值进行了指认.通过自然键轨道(NBO)分析,发现由钚到氧的电荷转移.相对于PuO和PuO2分子,在Pu2O3中形成较弱的Pu—O键.分析自旋布居,发现在这些分子中,自旋磁动量大都由Pu原子的5f电子贡献,而氧原子的2p轨道往往贡献反平行的自旋.     

原子分子在Ni(100)表面吸附的第一性原理研究

本文采用密度泛函理论,结合周期性平板模型,通过对原子H、N、O、S和C,分子CO、N2、NH3、NO,以及自由基CH3、CH、CH2、OH在Ni(100)表面吸附的研究,比较了它们的吸附能,稳定吸附位点,吸附结构及扩散能垒等信息.这些吸附质与表面结合能力从小到大依次是N2NH3COCH3NOHOHCH2CNSONCHC.在所有的原子中,O原子倾向于吸附在桥位,而其余的原子则倾向于吸附在空位.除N2之外的分子吸附物(CO、NO、NH3),最佳吸附位点均为四重空位,而N2的最稳定吸附位置为顶位.对于自由基吸附物(CH、CH2、CN、OH)而言,它们倾向于吸附在四重空位,而CH3则稳定吸附在桥位.     

光学气敏材料金红石相二氧化钛(110)面吸附CO分子的微观特性机理研究

利用光学气敏材料吸附气体,引起材料光学性质的变化来测量气体成分,是当前气敏传感研究领域的一个热点方向.本文针对光学气敏材料金红石相TiO2(110)表面吸附CO分子的微观特性进行研究,采用基于密度泛函理论(DFT)体系下的第一性原理平面波超软赝势方法,计算了表面的吸附能、电子态密度、光学性质和电荷密度的变化.结果表明:终止于二配位O原子的TiO2(110)面为最稳定表面,该表面吸附CO分子以C端吸附方式最为稳定,且氧空位浓度越高,越有助于对CO分子的吸附,吸附过程为放热.在氧空位浓度为33%时,吸附能达到1.319 eV,吸附后结构趋于更加稳定.表面吸附CO分子后,其实质是表面的氧空位氧化了CO分子,CO分子的电荷向材料表面转移.含有氧空位的表面吸附CO分子后都改善了其在可见光范围内的光学性质,但是氧空位浓度越高,改善其光吸收和反射能力越明显,光学气敏传感特性表现越显著.     

CO在尖晶石结构CuCr2O4(111)表面上的吸附理论研究

采用密度泛函理论，研究了CO在具有尖晶石结构的过渡金属氧化物CuCr2O4(100)表面上的吸附. 几何构型优化结果表明，CO倾向于以碳端吸附在Cu原子上，吸附能达到133.2 kJ/mol. 吸附在五配位的Cr原子上也比较稳定，吸附能为57.5 kJ/mol. 吸附后，C-O键伸长，振动频率出现红移，表明分子被活化. 同时分析了吸附前后态密度的变化，探讨了CO与底物的成键机理.     

A density functional theory study on the adsorption of CO and O₂ on Cu-terminated Cu₂O（111） surface

The adsorptions of CO and O2 molecules individually on the stoichiometric Cu-terminated Cu2O(111) surface are investigated by first-principles calculations on the basis of the density functional theory.The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of -1.69 eV,whereas the O2 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cu1 site,and has an adsorption energy of -1.97 eV.From the analysis of density of states,it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate.The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption,and overlaps substantially with bands of the adsorbed CO molecule.There is a broadening of the 2π orbital of the O2 molecule because of its overlapping with the Cu 3d orbital,indicating that strong 3d-2π interactions are involved in the chemisorption of the O2 molecule on the surface.     

A density functional theory study on the adsorption of CO and O2 on Cu-terminated Cu2O （111） surface

The adsorptions of CO and 02 molecules individually on the stoichiometric Cu-terminatcd Cu20 （111） surface are investigated by first-principles calculations on the basis of the density functional theory. The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of-1.69 eV, whereas the 02 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cul site, and has an adsorption energy of -1.97 eV. From the analysis of density of states, it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate. The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption, and overlaps substantially with bands of the adsorbed CO molecule. There is a broadening of the 2π orbital of the 02 molecule because of its overlapping with the Cu 3d orbital, indicating that strong 3d-2π interactions are involved in the chemisorption of the 02 molecule on the surface.     

First-principles study of molecular NO dissociation on Ir(100) surface

The dissociation of NO on Ir(100) surface is investigated using density functional theory (DFT). The pathway and transition state (TS) of the dissociation of NO molecule are determined using climbing image nudge elastic band (CI-NEB). The prerequisite state of NO dissociation is determining the most stable sites of the reactant and products. We found that the most energetically stable sites are the hollow for N atom and the bridge for NO molecule as well as O atom. We found that the bending of NO is the first step of the dissociation reaction due to the increase of the back-donation from the d-band of Ir to 2π ^? orbital of NO, which causes the weakening of NO bond. The dissociation energy barrier of NO molecule on Ir(100) surface is 0.49 eV.     

Molecular orbital study of the chemisorption of carbon monoxide on a tungsten (100) surface

The adsorption energies of carbon monoxide chemisorbed at various sites on a tungsten (100) surface have been calculated by extended Hückel molecular orbital theory (EHMO). The concept of a “surface molecule” in which CO is bonded to an array of tungsten atoms W_n has been employed. Dissociative adsorption in which C occupies a four-fold, five-coordination site and O occupies either a four- or two-fold site has been found to be the most stable form for CO on a W surface. Stable one-fold and two-fold sites of molecularly adsorbed CO have also been found in which the CO group is normal to the surface plane and the C atom is nearest the surface. Adsorption energies and molecular orbitals for the stable molecularly and dissociatively adsobred CO sites are compared with the experimental data on various types of adsorbed CO, i.e., virgin-, α-, and β-CO. Models are suggested for each of these adsorption types. The strongest bonding interactions occur between the CO 5σ orbital and the totally symmetric 5d and 6s orbitals of the W_n cluster. Possible mechanisms for conversion of molecularly adsorbed CO to dissociatively adsorbed CO are proposed and the corresponding activation energies are estimated.     

CO adsorption on oxygen-modified molybdenum surfaces

Structures of carbon monoxide layers on the oxygen-modified Mo(1 1 0) and Mo(1 1 2) surfaces have been investigated by means of density-functional (DFT) calculations. It is found that CO molecules adsorb at hollow sites on the O/Mo(1 1 0) surface and nearly atop Mo atoms on the O/Mo(1 1 2) surface. The favorable positions for adsorption are shown to be near protrusions of electron density above the Mo surface atoms. The presence of oxygen on the molybdenum surface significantly reduces the binding energy of the CO molecule with the substrate; on the oxygen-saturated Mo(1 1 0) surface, the adsorption of CO is completely blocked. The calculated local densities of states (LDOS) demonstrate that the O 2s peak for O adsorbed on Mo(1 1 0) surface is at −19 eV (with respect to the Fermi level), while for the oxygen atom of an adsorbed CO molecule the related 3σ molecular orbital gives rise to a peak at −23 eV. This difference stems from the bonding of the O atom either with Mo surface for adsorbed O or with C atom in adsorbed CO, and therefore the position of the O 2s peak in photoemission spectra can serve as a convincing argument in favor of either the presence or absence of the CO dissociation on Mo surfaces.     

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.     

Molecular cluster calculations for the interpretation of CO chemisorption on a Ni(100) surface

Self-consistent Hartree-Fock-Slater molecular cluster calculations for the chemisorption of carbon monoxide on a Ni(100) surface are presented. In earlier calculations of this type the CO molecule has been assumed to be chemisorbed in a hollow position of C_4v symmetry. A recent EELS experiment shows however that in the most stable configuration CO is linearly bonded to the Ni atoms, i.e. a top position of the CO-molecule. This experiment indicates also that there exists an additional bridge bonding of the CO molecule to the two nearest neighbour Ni atoms. The variation of the energy levels, binding energies and charge distribution with the height of the CO molecule above the nickel surface is calculated for the top position using the NiCO and Ni₅CO clusters and for the bridge bonding configuration using the Ni₂CO cluster. The CO 1π level is found to be split by about 0.8 eV in bridge bonding geometry. For both hollow and top positions the 1π and 5σ levels are separated by about 0.5 eV. The energy separation to the 4σ level is about 3 eV, which is in good agreement with experimental data. Theoretical ionization energies relative to the Fermi energy for top position geometry at a bond distance of 3.5 au between the carbon atom and nickel surface were found to be 25.7, 11.7, 8.7 and 8.2 eV for the 3σ, 4σ, 5σ and 1π levels which should be compared with the experimental data of 29.0, 10.8, 8.4 and 7.8 eV, respectively. The corresponding ionization energies for a bond angle of 99° in bridge bonding were 23.7, 12.1, 7.3, 7.0 and 7.9 eV. The two last values represent the 1π level which is split into two levels in this geometry. The variation of the C-O stretch vibrational frequencies with the height of the CO molecule above the surface for the top-position geometry is estimated from the 5σ and 2π gross orbital populations and from the CO σ and π overlap populations.     

Unique geometric and electronic structure of CO adsorbed on Ge(100): A DFT study

CO adsorption on the Ge(100) surface has been investigated using a slab model with density functional theory implemented in SIESTA. CO was found to be exclusively adsorbed on the asymmetric dimer with C attaching on the lower Ge dimer atom. The adsorption process is barrierless. The calculated adsorption energy and vibration frequencies are comparable to previous experimental results. The crystal orbital Hamilton analysis showed that the bonding between Ge and CO is mainly attributable to the Ge 4p_z orbital overlapping with C 2 s, or with CO molecular orbitals 3σ and 4σ. The repulsive energy between adsorbed CO molecules is less than 1 kcal/mol. The diffusion barrier of CO on the Ge(100) surface is about 14 kcal/mol.