Electronic structures and coronene on Ru（0001）： vibrational properties of first-principles study

We calculate the configurations,electronic structures,vibrational properties at the coronene/Ru(0001) interface,and adsorption of a single Pt atom on coronene/Ru(0001) based on density functional theory calculations.The geometric structures and electronic structures of the coronene on Ru(0001) are compared with those of the graphene/Ru(0001).The results show that the coronene/Ru(0001) can be a simplified model system used to describe the interaction between graphene and ruthenium.Further calculations of the vibrational properties of coronene molecule adsorbed on Ru(0001) suggest that the phonon properties of differently corrugated regions of graphene on Ru(0001) are different.This model system is also used to investigate the selective adsorption of Pt atoms on graphene/Ru(0001).The configurations of Pt on coronene/Ru(0001) with the lowest binding energy give clues to explain the experimental observation that a Pt cluster selectively adsorbs on the second highest regions of graphene/Ru(0001).This work provides a simple model for understanding the adsorption properties and vibrational properties of graphene on Ru(0001) substrate.     

First-principles study of the （001） surface of cubic PbHfO3 and BaHfO3

Using first-principles techniques,we investigate the(001) surfaces of cubic PbHfO3(PHO) and BaHfO3(BHO) terminated with both AO(A=Pb and Ba) and HfO2.Surface structure,partial density of states,band structure,and surface energy are obtained.The BaO surface is found to be similar to its counterpart in BHO.For the HfO2-terminated surface of cubic PHO,the largest relaxation appears on the second-layer atoms but not on the first-layer ones.The analysis of the structure relaxation parameters reveals that the rumpling of the(001) surface for PHO is stronger than that for BHO.The surface thermodynamic stability is explored,and it is found that both the PbO-and the BaO-terminated surfaces are more stable than the HfO2-terminated surfaces for PHO and BHO,respectively.The surface energy calculations show that the(001) surface of PHO is more easily constructed than that of BHO.     

CO adsorption on small Aun（n=1-7） clusters supported on a reduced rutile TiO2（110） surface:a first-principles study

CO adsorption on small Au n(n = 1-7) clusters which are supported by a partially reduced rutile TiO 2(110) surface has been investigated by the first-principles method.The low coordinated sites of Au clusters are favorable for CO adsorption.CO-Au n-TiO 2 system displays surface magnetism.There is a strong interaction between the adsorbed CO molecule and the supported Au clusters.     

First-principles calculations of 5d atoms doped hexagonal-AlN sheets：Geometry,magnetic property and the influence of symmetry and symmetry-breaking on the electronic structure

The geometry, electronic structure and magnetic property of the hexagonal AlN(h-AlN) sheet doped by 5d atoms(Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the density functional theory. The influence of symmetry and symmetry-breaking is also studied. There are two types of local symmetries of the doped systems: C3v and D3h. The symmetry will deviate from exact C3v and D3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0μBfor Lu, Ta and Ir; 1μB for Hf, W, Pt and Hg; 2μB for Re and Au; and 3μB for Os and Al-vacancy. The total densities of state are presented, where impurity energy levels exist. The impurity energy levels and total magnetic moments can be explained by the splitting of 5d orbitals or molecular orbitals under different symmetries.     

A density-functional theory investigation on desorption of O2 on Sn（111） and its comparison with initial oxidation on the X（111） （X=Si,Ge, Sn,Pb） surfaces

<正>The first-principles calculations are performed to investigate the adsorption of O₂ molecules on an Sn（111） 2×2 surface.The chemisorbed adsorption precursor states for O₂ are identified to be along the parallel and vertical channels, and the surface reconstructions of Sn（lll） induced by oxygen adsorption are studied.Based on this,the adsorption behaviours of O₂ on X（111）（X=Si,Ge,Sn,Pb） surfaces are analysed,and the most stable adsorption channels of O₂ on X（111）（X=Si,Ge,Sn,Pb） are identified.The surface reconstructions and electron distributions along the most stable adsorption channels are discussed and compared.The results show that the O₂ adsorption ability declines gradually and the amount of charge transferred decreases with the enhancement of metallicity.     

Ar adsorptions on Al （111） and Ir （111） surfaces： a first-principles study

We investigate the adsorptions of Ar on Al (111) and Ir (111) surfaces at the four high symmetry sites,i.e.,top,bridge,fcc-and hcp-hollow sites at the coverage of 0.25 monolayer (ML) using the density functional theory within the generalized gradient approximation of Perdew,Burke and Ernzerhof functions.The geometric structures,the binding energies,the electronic properties of argon atoms adsorbed on Al (111) and Ir (111) surfaces,the difference in electron density between on the Al (111) surface and on the Ir (111) surface and the total density of states are calculated.Our studies indicate that the most stable adsorption site of Ar on the Al (111) surface is found to be the fcc-hollow site for the (2 × 2) structure.The corresponding binding energy of an argon atom at this site is 0.538 eV/Ar atom at a coverage of 0.25 ML.For the Ar adsorption on Ir (111) surface at the same coverage,the most favourable site is the hcp-hollow site,with a corresponding binding energy of 0.493 eV.The total density of states (TDOS) is analysed for Ar adsorption on Al (111) surface and it is concluded that the adsorption behaviour is dominated by the interaction between 3s,3p orbits of Ar atom and the 3p orbit of the base Al metal and the formation of sp hybrid orbital.For Ar adsorption on Ir (111) surface,the conclusion is that the main interaction in the process of Ar adsorption on Ir (111) surface comes from the 3s and 3p orbits of argon atom and 5d orbit of Ir atom.     

Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ spinels： A first-principles study

<正>Structural and magnetic properties of LiNi_0.5Mn_1.5O₄ and LiNi_0.5Mn_1.5O_4-δ are investigated using densityfunctional theory calculations.Results indicate that nonstoichiometric LiNi_0.5Mn_1.5O_4-δ and stoichiometric LiNi_0.5Mn_1.5O₄ exhibit two different structures,i.e.,the face-centred cubic（Fd-3m） and primitive,or simple,cubic （P4₃32） space groups,respectively.It is found that the magnetic ground state of LiNi_0.5Mn_1.5O₄（P4₃32 and Fd-3m） is a ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the[110]direction whereas they are antiferromagnetic with respect to each other.We demonstrate that it is the presence of an O-vacancy in LiNi_0.5Mn_1.5O_4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi_0.5Mn_1.5O₄ with the P4₃32 space group.     

Water adsorption on the Be（0001） surface： from monomer to trimer adsorption

In this paper,the density functional theory has been used to perform a comparative theoretical study of water monomer,dimer,trimer,and bilayer adsorptions on the Be(0001) surface.In our calculations,the adsorbed water molecules are energetically favoured adsorbed on the atop sites,and the dimer adsorption is found to be the most stable with a peak adsorption energy of ～ 437 meV.Further analyses have revealed that the essential bonding interaction between the water monomer and the metal substrate is the hybridization of the water 3a 1-like molecular orbital with the (s,p z) orbitals of the surface beryllium atoms.While in the case of the water dimer adsorption,the 1b 1-like orbital of the H2O molecule plays a dominant role.     

Step instability of the In0.2Ga0.8As （001） surface during annealing

Anisotropic evolution of the step edges on the compressive-strained In0.2Ga0.8 As/GaAs(001) surface has been investigated by scanning tunneling microscopy (STM). The experiments suggest that step edges are indeed sinuous and protrude somewhere a little way along the [110] direction, which is different from the classical waviness predicted by the theoretical model. We consider that the monatomic step edges undergo a morphological instability induced by the anisotropic diffusion of adatoms on the terrace during annealing, and we improve a kinetic model of step edge based on the classical Burton–Cabrera–Frank (BCF) model in order to determine the normal velocity of step enlargement. The results show that the normal velocity is proportional to the arc length of the peninsula, which is consistent with the first result of our kinetic model. Additionally, a significant phenomenon is an excess elongation along the [110] direction at the top of the peninsula with a higher aspect ratio, which is attributed to the restriction of diffusion lengths.     

Methane adsorption on graphite（0001） films： A first-principles study

Using first-principles methods, we have systematically investigated the electronic density of states, work function, and adsorption energy of the methane molecule adsorbed on graphite(0001) films. The surface energy and the interlayer relaxation of the clean graphite(0001) as a function of the thickness of the film were also studied. The results show that the interlayer relaxation is small due to the weak interaction between the neighboring layers. The one-fold top site is found most favourable on substrate for methane with the adsorption energy of 133 meV. For the adsorption with different adsorption heights above the graphite film with four layers, the methane is found to prefer to appear at about 3.21 A above the graphite. We also noted that the adsorption energy does not dependent much on the thickness of the graphite films. The work function is enhanced slightly by adsorption of methane due to the slight charge transfer from the graphite surface to the methane molecule.     

Comparisons between adsorption and diffusion of alkali,alkaline earth metal atoms on silicene and those on silicane:Insight from first-principles calculations

The adsorption and diffusion behaviors of alkali and alkaline-earth metal atoms on silicane and silicene are both investigated by using a first-principles method within the frame of density functional theory.Silicane is staler against the metal adatoms than silicene.Hydrogenation makes the adsorption energies of various metal atoms considered in our calculations on silicane significantly lower than those on silicene.Similar diffusion energy barriers of alkali metal atoms on silicane and silicene could be observed.However,the diffusion energy barriers of alkali-earth metal atoms on silicane are essentially lower than those on silicene due to the small structural distortion and weak interaction between metal atoms and silicane substrate.Combining the adsorption energy with the diffusion energy barriers,it is found that the clustering would occur when depositing metal atoms on perfect hydrogenated silicene with relative high coverage.In order to avoid forming a metal cluster,we need to remove the hydrogen atoms from the silicane substrate to achieve the defective silicane.Our results are helpful for understanding the interaction between metal atoms and silicene-based two-dimensional materials.     

氧在Nb(110)表面吸附的第一性原理研究

通过第一性原理赝势平面波方法研究了氧在Nb(110)表面的吸附性质随覆盖度变化规律. O在Nb(110)表面最稳定吸附位是洞位,次稳定吸附位是长桥位. 在长桥位吸附时, O诱导Nb(110)表面功函数随覆盖度的增加而几乎线性增加;但当O在洞位吸附时, 与干净Nb表面相比, 覆盖度为0.75 ML和1.0 ML时功函数增加, 而覆盖度为0.25 ML和0.5 ML时功函数减小.通过对面平均电荷密度分布和偶极矩变化的讨论, 解释了由吸附导致功函数复杂变化的原因.通过对表面原子结构和态密度分析, 讨论了O在Nb表面吸附时引起表面原子结构变化以及O和Nb(110)表面原子的相互作用.     

Influence of Pb adatom on adsorption of oxygen molecules on Pb(111) surface: a first-principles study

Using first-principles calculations, we systematically study the influence of Pb adatom on the adsorption and the dissociation of oxygen molecules on Pb(111) surface, to explore the effect of a point defect on the oxidation of the Pb(111) surface. We find that when an oxygen molecule is adsorbed near an adatom on the Pb surface, the molecule will be dissociated without any obvious barriers, and the dissociated O atoms bond with both the adatom and the surface Pb atoms. The adsorption energy in this situation is much larger than that on a clean Pb surface. Besides, for an adsorbed oxygen molecule on a clean Pb surface, a diffusing Pb adatom can also change its adsorption state and enlarge the adsorption energy for O, but it does not make the oxygen molecule dissociated. And in this situation, there is a molecule-like PbO2 cluster formed on the Pb surface.     

InSb(110)表面S,O原子吸附的第一性原理研究

基于第一性原理方法, 采用广义梯度近似的交换关联势, 对InSb材料(110)表面的硫吸附和氧吸附之后体系性质的差异进行了分析. 讨论了两种吸附下的键长、键角、能带结构和态密度的变化, 从理论上论证了硫吸附比氧吸附对InSb红外探测器表面态的钝化有优越性, 有利于工艺上在钝化时的选择. 关键词： 第一性原理 InSb 硫吸附 氧吸附     

Topological properties of Sb(111) surface: A first-principles study

First-principles calculations based on the density functional theory were performed to systematically study the electronic properties of the thin film of antimony in (111) orientation. By considering the spin-orbit interaction, for stoichiometric surface, the topological states keep robust for six-bilayer case, and can be recovered in the three-bilayer film, which are guaranteed by time-reversal symmetry and inverse symmetry. For reduced surface doped by non-magnetic Bi or magnetic Mn atom, localized three-fold symmetric features can be identified. Moreover, band structures show that the non-trivial topological states stand for non-magnetic substitutional Bi atom, while can be eliminated by adsorbed or substitutional magnetic Mn atom.     

Electronic structures and vibrational properties of coronene on Ru(0001): first-principles study

We calculate the configurations, electronic structures, vibrational properties at the coronene/Ru(0001) interface, and adsorption of a single Pt atom on coronene/Ru(0001) based on density functional theory calculations. The geometric structures and electronic structures of the coronene on Ru(0001) are compared with those of the graphene/Ru(0001). The results show that the coronene/Ru(0001) can be a simplified model system used to describe the interaction between graphene and ruthenium. Further calculations of the vibrational properties of coronene molecule adsorbed on Ru(0001) suggest that the phonon properties of differently corrugated regions of graphene on Ru(0001) are different. This model system is also used to investigate the selective adsorption of Pt atoms on graphene/Ru(0001). The configurations of Pt on coronene/Ru(0001) with the lowest binding energy give clues to explain the experimental observation that a Pt cluster selectively adsorbs on the second highest regions of graphene/Ru(0001). This work provides a simple model for understanding the adsorption properties and vibrational properties of graphene on Ru(0001) substrate.     

First-principles study of diffusion behaviour of point defects in the O-terminated (0001) surface in wurtzite ZnO

A detailed first-principles study of the diffusion behaviour of point defects in the O-terminated (0001) surface in wurtzite ZnO was performed. The O vacancy and interstitial are found to diffuse much more easily in surface than in bulk. The Zn vacancy has a similar migration barrier for both bulk and surface, but has much smaller barrier for the diffuse-in process. The Zn interstitial is difficult to diffuse in the surface directly, but it can diffuse into the bulk relatively easily. Specific values of corresponding migration barriers are obtained.     

Stability and diffusion properties of self-interstitial atoms in tungsten:a first-principles investigation

Employing a first-principles method based on the density function theory,we systematically investigate the structures,stability and diffusion of self-interstitial atoms(SIAs) in tungsten(W).The <111> dumbbell is shown to be the most stable SIA defect configuration with the formation energy of ~9.43 eV.The on-site rotation modes can be described by a quite soft floating mechanism and a down-hill "drift" diffusion process from <110> dumbbell to <111> dumbbell and from <001> dumbbell to <110> dumbbell,respectively.Among different SIA configurations jumping to near neighboring site,the <111> dumbbell is more preferable to migrate directly to first-nearest-neighboring site with a much lower energy barrier of 0.004 eV.These results provide a useful reference for W as a candidate plasma facing material in fusion Tokamak.     

A first-principles study of surface and subsurface H on and in Ni(1 1 1): diffusional properties and coverage-dependent behavior

Periodic, self-consistent, density functional theory (GGA-PW91) calculations are performed for both surface and subsurface atomic hydrogen on and in Ni(1 1 1). At a low coverage (θ=0.25 ML), the binding energies (BEs) of a hydrogen atom in surface fcc, subsurface octahedral (first layer), and subsurface octahedral (second layer) sites are −2.89, −2.18, and −2.11 eV, respectively. The activation energy barriers for hydrogen diffusion from the surface to the first subsurface layer and from the first to the second subsurface layer are estimated to be 0.88 and 0.52 eV, respectively. In the entire coverage range studied, hydrogen occupies surface fcc and hcp sites and subsurface octahedral sites. In addition, the magnitude of the BE per hydrogen atom and the magnetization of the nickel slabs both decrease as hydrogen coverage increases. Vibrational frequencies of hydrogen at various surface and subsurface sites are calculated and are in reasonable agreement with experimental data. A phase stability calculation with a 2 × 2 surface unit cell shows that a p(2 × 2)-2H overlayer structure (θ=0.5 ML) and a p(1 × 1)-1H structure (θ=1.0 ML) are stable at low hydrogen pressures, in agreement with numerous experimental results. A very large increase in pressure is required to populate subsurface sites. After such an increase occurs, the first subsurface layer is filled completely.