First principles calculations of relationship between the Cu surface states and relaxations

In this paper the relationship between the surface relaxations and the electron density distributions of surface states of Cu(100), Cu(110), and Cu(111) surfaces is obtained by first-principles calculations. The calculations indicate that relaxations mainly occur in the layers at which the surface states electrons are localized, and the magnitudes of the multilayer relaxations correspond to the difference of electron density of surface states between adjacent layers. The larger the interlayer relaxation is, the larger the difference of electron density of surface states between two layers is.     

Multilayer relaxation of fcc metals (001) surface: A modified embedded atom method study

The (001) surface multilayer relaxation results calculated by the modified embedded atom method (MEAM) show that Ni, Al, Rh and Ir (001) surface are ‘anomalous’ outward relaxation, while Cu, Ag, Au, Pd, Pt and Pb (001) surface are inward relaxation. For the inward relaxation metals, the relaxation between the first two layers increase for the 3d, 4d and 5d metals at the same column in the periodic table, successively. The expansion (contraction) between the first two layers at fcc (001) surfaces is accompanied by the decrease (increase) in the electronic density at the lattice of the first two layers. The surface energies results show that the surface energies decrease for all fcc (001) surfaces due to relaxation, whereas the changes not more than 5%.     

Lattice relaxation at alkali metal surfaces

The surface relaxation of the first interlayer spacing for both the (110) and (100) faces of alkali metals has been calculated selfconsistently using the density functional formalism and a new density matrix method which obviates the use of wavefunctions. For the (110) surfaces of all alkali metals we find no or only very small relaxation. The (100) surfaces show bigger relaxation effects and these vary from 3.5% inward for Li to 1% outward for Cs. These findings are consistent with general trends found in LEED or Ion scattering studies. Force constants for the movement of the last atomic layer are also determined.     

Cu 表面性质的第一性原理分析

采用第一性原理赝势平面波方法, 计算并详细分析了面心立方Cu晶体及其 (100), (110) 和 (111) 这3个低指数表面的原子结构、 表面能量及表面电子态密度. 表面能的计算结果表明, Cu (111) 表面的结构稳定性最好, Cu (100) 表面次之, Cu (110)表面的结构稳定性最差. 3个表面的表面原子弛豫量随着层数的增加而逐渐减弱. Cu (110) 表面的最表层原子相对收缩最大, Cu (100)表面次之, Cu (111) 表面的最表层原子相对收缩最小. 表面原子弛豫不仅引起表面几何结构的变化, 而且使表面层原子的电子态密度峰形相对晶体内部发生变化, 这是表面能产生的主要原因, 而Cu (110)表面相对于Cu (100)与Cu (111)表面具有高表面活性的主要原因则源于其表面层原子电子态密度在高能级处的波峰相对晶体内部显著的升高. 关键词： Cu 晶体 表面结构 表面能 态密度     

Au(110)表面结构和氧原子吸附的第一性原理研究

用密度泛函理论(DFT)研究了金属Au(110)表面结构以及氧原子的吸附状态.计算得到Au(110)-(1×2)缺列再构表面原子的弛豫分别是-15.0%(Δd₁₂/d₀)和-1.1%(Δd₂₃/d₀),表面能为52.7 meV/²,功函数Φ=5.00 eV;Au(110)-(1×3)缺列再构表面的Δd_{1 关键词： 缺列再构Au(110)表面 STM图像 氧原子吸附}     

Electronic structure of the (111) and (111) surfaces of GaAs

Inward relaxation effects of the outermost Ga layer on the electronic structure of GaAs (111) Ga and outward expansion effects of the outermost As layer on that of GaAs ($\text{111}$) As are studied by extended Hückel theory. Three different surface geometries are examined for the respective surfaces. It is shown that upon relaxation on GaAs (111) or upon expansion on GaAs ($\text{111}$) new surface states associated with dangling- and back-bonds are revealed. The character and dispersion behaviour of strongly localized surface states are described.     

The (100), (111) and (110) surfaces of diamond: an ab initio B3LYP study

We present an accurate ab initio study of the structure and surface energy of the low-index (100), (111) and (110) diamond faces, by using the hybrid Hartree–Fock/density functional B3LYP Hamiltonian and a localised all-electron Gaussian-type basis set. A two-dimensional periodic slab model has been adopted, for which convergence on both structural and energetic parameters has been thoroughly investigated. For all the three surfaces, possible relaxations and reconstructions have been considered; a detailed geometrical characterisation is provided for the most stable structure of each orientation. Surface energy is discussed for all the investigated faces.     

Cluster model approach for electronic structure of Si and Ge(111) and GaAs(110) surfaces

For the purpose of exploring how realistic a cluster model can be for semiconductor surfaces, extended Huckel theory calculations are performed on clusters modeling Si and Ge(111) and GaAs(110) surfaces as prototypes. Boundary conditions of the clusters are devised to be reduced. The ideal, relaxed, and reconstructed Si and Ge(111) surfaces are dealt with. Hydrogen chemisorbed (111) clusters of Si and Ge are also investigated as prototypes of chemisorption systems. Some comparison of the results with finite slab calculations and experiments is presented. The cluster-size dependence of the calculated energy levels, local densities of states, and charge distributions is examined for Si and Ge(111) clusters. It is found that a 45-atom cluster which has seven layers along the [111] direction is large enough to identify basic surface states and study the hydrogen chemisorption on Si and Ge(111) surfaces. Also, it is presented that surface states on the clean Si and Ge(111) clusters exist independent of relaxation. Further, the calculation for the relaxed GaAs(110) cluster gives the empty and filled dangling-orbital surface states comparable to experimental data and results of finite slab calculations. The cluster approach is concluded to be a highly useful and economical one for semiconductor surface problems.     

Oxygen adsorption on the LaB6(100), (110) and (111) surfaces

Oxygen adsorption on the LaB₆(100), (110) and (111) clean surfaces has been studied by means of UPS, XPS and LEED. The results on oxygen adsorption will be discussed on the basis of the structurs and the electronic states on the LaB₆(100), (110) and (111) clean surfaces. The surface states on LaB₆(110) disappear at the oxygen exposure of 0.4 L where a c(2 × 2) LEED pattern disappears and a (1 × 1) LEED pattern appears. The work function on LaB₆(110) is increased to ～3.8 eV by an oxygen exposure of ～2 L. The surface states on LaB₆(111) disappear at an oxygen exposure of ～2 L where the work function has a maximum value of ～4.4 eV. Oxygen is adsorbed on the surface boron atoms of LaB₆(111) until an exposure of ～2 L. Above this exposure, oxygen is adsorbed on another site to lower the work function from ～4.4 to ～3.8 eV until an oxygen exposure of ～100L. The initial sticking coefficient on LaB₆(110) has the highest value of ～1 among the (100), (110) and (111) surfaces. The (100) surface is most stable to oxygen among these surfaces. It is suggested that the dangling bonds of boron atoms play an important role in oxygen adsorption on the LaB₆ surfaces.     

Electric-dipole layer on Au(111) surfaces

We measured the barrier height (BH) a UHV scanning tunneling microscope on Au(111) surfaces with Au, Pt, and carbon nanotube tips. The 222?{^[¯] }3^[¯]\sqrt\Box3\Box]] reconstruction was observed with all the tips, and the current-voltage relation reflected the density of states of the tips. The BH measured on the reconstructed Au(111) surface using a modulation method showed a bias-polarity dependence as 30%, at low currents (<100 pA) irrespective of the tip material, while on unreconstructed Au surfaces, BH values were independent of the bias polarity, suggesting a dipole layer originating from the reconstructed Au(111) surface.     

Structural,electronic and magnetic properties of the (001), (110) and (111) surfaces of rocksalt sodium sulfide: A first-principles study

First principles study of the structural, electronic and magnetic properties of the (111), (110) and (001) surfaces of rocksalt sodium sulfide (rs-NaS) are reported. The results show that the bulk half-metallicity of this compound is well preserved on the surfaces considered here except for Na-terminated (111) surface. The spin-flip gap at the S-terminated (111), (001) and (110) surfaces are close to the bulk value. Using ab-initio atomistic thermodynamics, we calculate the surface energies as a function of chemical potential to find the most stable surface. We find that the Na-terminated (111) surface is the most stable one over the whole allowed range of chemical potential, while the surface energies of the (001) and (110) surfaces approach the most stable surface energy at the sulfur rich environment. We have also calculated the interlayer exchange interaction in bulk and Na-terminated (111) surface by classical Heisenberg model and we found that the surface effects do not change these kinds of interactions significantly.     

First-Principles Study of Electronic Properties in PbS（1^-00） with Vacancy Defect

Electronic properties of both Pb and S vacancy defects in PbS（1^-00） have been studied using the first-principles density functional theory （DFT） calculations with the plane-wave pseudopotentials. It is found that the density of states （DOS） near the top of the valence band and the bottom of the conduction band is significantly modified by these defects. Our calculation indicates that in the case of S vacancy defects the Fermi energy shifts to the conduction band making it as an n-type PbS （donor）. However, in the case of Pb vacancy, because of the appreciable change of the DOS, the system acts as a p-type PbS （accepter）. In addition, the structural relaxation shows that the defect leads to outward relaxation of the nearest-neighbouring atoms and inward relaxation of the next-nearest neighbouring atoms.     

Ion-beam crystallography of clean and sulfur covered Ni(110)

Medium energy ion scattering has been used to determine the atomic structure of a Ni(110) surface covered with 0.5 monolayer of sulfur. After having confirmed that the sulfur atom resides in a fourfold-coordinated hollow site, it was found that its distance above the plane of the first Ni layer is 0.87 ± 0.03 Å. We measured a 6 ± 3% outward relaxation effect for the sulfur covered Ni(110) surface layer and an inward relaxation of 4 ± 1% when this surface is clean.     

Cu台阶面多层弛豫的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法对Cu(311),(511),(331)和(221)四个高指数台阶表面的弛豫结构和弛豫后表面各层的电子特性进行了系统研究.发现四个台阶面的层间弛豫规律依次为-+-…,--+-…,--+-…和---+-…,与其平台-阶梯n(hkl)×(uvw)的表示法2(100)×(111),3(100)×(111),3(111)×(111)和4(111)×(111)中的原子排数n相关,即     

Electron states and atomic positions at the {001}, {110} and {111} faces of W and Mo

The results of ab initio calculations on the {001}, {110} and {111} surfaces of W and Mo and on the (√2 × √2)R45° reconstructed W {001} surface are presented. A distribution of surface states in reasonable agreement with experiment is found. A simple parametrisation of the short range repulsive force between transition metal atoms is used to predict, for all these surfaces, relaxations which are comparable with those observed. This same parametrisation indicates that the W and Mo {001} surfaces are stable to proposed reconstructive displacements.     

Local density of states of GaAs and InAs surfaces: Ideal (111), (001) and (110) surfaces and monoatomic steps on the (111) and the (001) surface

The ideal (111), (001) and (110) surfaces of GaAs and InAs are investigated by means of the LCAO Green function recursion method to obtain local density of states. Main emphasis is laid on the analysis of the nature and character of the inherent surface states. For this purpose, several imperfections on the (111) and the (001) surface (i.e. vacancies and steps with varying topology) are treated to demonstrate the local character of Shockley surface states and to confirm their chemical nature. The applicability of the results obtained to other A³B⁵ compounds is discussed. Comparison with experiment and other theoretical investigations is also made.     

用低能电子衍射研究ⅢA-ⅤA和ⅡB-ⅥA化合物(110)和(1010)表面的弛豫

用低能电子衍射研究了ⅢA-VA和ⅡB-VIA化合物(110)和(1010)表面的弛豫,发现当理论计算与实验符合得很好时其结构是:保持表面上A-B键长不变,用一个旋转角ω,使B原(离)子向外移动,A原(离)子向内移动,第一表面原子层间距d₁=0.610-0.810?[对ⅢA-VA(110)],0.536—0.825?[对ⅡB-VIA(110)]和0.633-1.060?[对ⅡB-VIA(1010),第二表面原子层间距d₂=1.300-1.610?[对ⅢA-VA(100)],1.430-1.700?[对ⅡB-VIA(110)]和0.820-0.930?[对ⅡB-VIA(1010),而第三表面原子层间距d₃=1.410-2.440?[对ⅢA-VA(110)],2.020-2.250?[对ⅡB-VIA(110)]和1.910-2.440?[对ⅡB-VIA(1010)]。对此结构,弛豫率α是:0.24±0.02[对ⅢA-VA(110)],0.25±0.02[对ⅡB-VIA(1010)]和0.33±0.03[对ⅡB-VIA(1010)]。 关键词：     

Al吸附在Pt,Ir和Au的(111)面的低覆盖度研究

应用密度泛函理论,系统研究了Al原子在Pt(111),Ir(111)和Au(111)表面的桥位、顶位、三重面心立方(fcc)洞位和六角密排(hcp)洞位这四个典型位置的吸附情况. 主要计算了三吸附体系的几何结构、平均结合能和差分电荷密度,并系统讨论了相关原子的密立根电荷布居数和投影态密度.研究发现,对于Pt(111)和Ir(111)表面,Al原子在hcp洞位最稳定,但是对于Au(111)表面,Al原子在fcc洞位最稳定. 关键词： 吸附 密度泛函理论 结合能 电子结构     

Ionic and radical adsorption on the Au(hkl) surfaces: A DFT study

Adsorption of several ionic and non-ionic species (OH^?, O, O^?, O^2?, H, H⁺ and H^?) on the low-index Miller Au(hkl) surfaces has been investigated by means of density functional theory based methods. The stability order for adsorptions on the three surfaces decreases with the increasing of the coordination number of the outermost gold atoms in each surface, i.e., Au(110) > Au(100) > Au(111), which is in agreement with the experimental evidences. The detailed COOPs analysis of the various adsorption sites for all adsorbates in the surface with the most stable adsorption(s), Au(110), evidenced that adsorption in the gold surfaces may be a function of particle size and charge and substantiates the variability in the order of preferences sites for the adsorption of the different species found in these low-index Miller Au(hkl) surfaces. This variability increases with the increasing of the stability of the adsorptions on the gold surfaces, i.e., the Au(110) presents more variability in the order of preferences sites for the adsorption of different species.