Structural,electronic,and magnetic properties of transition-metal atom adsorbed two-dimensional GaAs nanosheet

By using first-principles calculations within the framework of density functional theory,the electronic and magnetic properties of 3d transitional metal(TM) atoms(from Sc to Zn) adsorbed monolayer Ga As nanosheets(Ga As NSs) are systematically investigated.Upon TM atom adsorption,Ga As NS,which is a nonmagnetic semiconductor,can be tuned into a magnetic semiconductor(Sc,V,and Fe adsorption),a half-metal(Mn adsorption),or a metal(Co and Cu adsorption).Our calculations show that the strong p–d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the Ga As NSs with Sc,V,and Fe adsorption.However,the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit,resulting in a stronger exchange interaction.Our results may be useful for electronic and magnetic applications of Ga As NS-based materials.     

Structural, electronic, and magnetic properties of bcc iron surfaces

Trends in atomic multilayer relaxations, surface energy, electronic work function, and magnetic structure of several low-Miller-index surfaces of iron are investigated employing density functional theory total energy calculations. The calculated topmost layer relaxations reproduce well the experimental contractions and their variation with the surface crystallographic orientation, and surface roughness. The multilayer relaxation sequences correlate with the reduced coordination in surface layers and can be explained in terms of a simple electrostatic picture. The surface energies scale almost linearly with the surface roughness. They agree well with the experimental surface tensions and show a small anisotropy in agreement with predictions based on measurements for other metals. The equilibrium shape of a bcc Fe crystal is determined and discussed. The work function anisotropy is calculated and rationalized in terms of changes in the valence charge distribution. Significantly increased local magnetic moments of atoms in the surface region are determined. The correlation between the anisotropy of the surface magnetic moments and atomic coordination in the outermost layers is demonstrated to follow a simple rule.     

Self-consistent LMTO approach to the electronic structure of semi-conductors: GaAs

The self-consistent Lineat Muffin Tin Orbital (LMTO) energy band method is applied to the case of the open structures (zinc blende) usual for many semi-conductors using GaAs as an example. Empty spheres are inserted into the most open parts of the structure and each sphere is assigned a spherically symmetric potential. The resulting band structure, density-of-state functions and XPS spectra (including matrix elements) are presented. Good agreement with more elaborate ab initio band results as well as with experiment is found. We conclude that the self-consistent LMTO approach using empty spheres provides a very efficient scheme for studying open structures.     

The relation between the electronic and magnetic structures of manganites in the tight-binding approximation

Analytic expressions for the dispersion curves E(k) of RMnO₃ (R=La, Pr, Nd, Sm, and other RE elements) have been obtained in the tight-binding approximation for the main types of magnetic ordering on the Mn sublattice. The first calculation of E(k) taking into account the oxygen subsystem and mutual ordering of the manganese and RE sublattices is reported. The results obtained permit a qualitative interpretation of some features observed in the behavior of the rare-earth manganites. Fiz. Tverd. Tela (St. Petersburg) 41, 2179–2182 (December 1999)     

几种三元过渡金属碳化物弹性及电子结构的第一性原理研究

基于密度泛函理论平面波方法研究了六方WC型Re_xW_1－xC(x=1, 0.25, 0.75, 0),Re_0.5Os_0.5C和Os_0.5W_0.5C的晶体结构、弹性和电子结构性质.研究发现Re_0.25W_0.75C晶体具有优异的弹性性能及稳定性,其剪切模量(312 GPa)超过了所有其他实验合成和     

Structural and electronic properties of transition-metal chalcogenides Mo_5S_4 nanowires

Transition-metal chalcogenide nanowires(TMCN) as a viable candidate for nanoscale applications have been attracting much attention for the last few decades. Starting from the rigid building block of M_6 octahedra(M = transition metal),depending on the way of connection between M_6 and decoration by chalcogenide atoms, multiple types of extended TMCN nanowires can be constructed based on some basic rules of backbone construction proposed here. Note that the well-known Chevrel-phase based M_6X_6 and M_6X_9(X = chalcogenide atom) nanowires, which are among our proposed structures, have been successfully synthesized by experiment and well studied. More interestingly, based on the construction principles, we predict three new structural phases(the cap, edge, and CE phases) of Mo_5S_4, one of which(the edge phase) has been obtained by top-down electron beam lithography on two-dimensional MoS_2, and the CE phase is yet to be synthesized but appears more stable than the edge phase. The stability of the new phases of Mo_5S_4 is further substantiated by crystal orbital overlapping population(COOP), phonon dispersion relation, and thermodynamic calculation. The barrier of the structural transition between different phases of Mo_5S_4 shows that it is very likely to realize an conversion from the experimentally achieved structure to the most stable CE phase. The calculated electronic structure shows an interesting band nesting between valence and conduction bands of the CE Mo_5S_4 phase, suggesting that such a nanowire structure can be well suitable for optoelectronic sensor applications.     

Manifestations of quasi-one-dimensional correlations in the electronic properties of transition-metal oxides

As follows from the string model, the pseudogap anomalies in the electronic properties of lightly doped cuprates, observed by different methods, can be explained by the segregation of charge carriers into bosonic stripes. The comparative investigation of the similar anomalies revealed in several “copperless” transition-metal oxides reliably suggests that these anomalies are likely to be due to the analogous processes of quasione-dimensional structurization of paired charge carriers into a metastable network of conducting nanochannels.     

Scaling properties of adsorption energies for hydrogen-containing molecules on transition-metal surfaces

Density functional theory calculations are presented for CHx, x=0,1,2,3, NHx, x=0,1,2, OHx, x=0,1, and SHx, x=0,1 adsorption on a range of close-packed and stepped transition-metal surfaces. We find that the adsorption energy of any of the molecules considered scales approximately with the adsorption energy of the central, C, N, O, or S atom, the scaling constant depending only on x. A model is proposed to understand this behavior. The scaling model is developed into a general framework for estimating the reaction energies for hydrogenation and dehydrogenation reactions.     

Solid surfaces: Their atomic,electronic and macroscopic properties

The free surface of a solid represents the most radical discontinuity in its structure that one can envisage. With crystalline solids the specific surface properties that arise involve à number of challenging physical problems as well as providing opportunities for exploitation in the electronics and chemical industries.

For convenience one may divide these surface characteristics into atomic, electronic and macroscopic effects but, in fact, they are all interrelated. As far as atomic structure is concerned the atomic spacing of the surface layer is usually different from that of the bulk. Further, the atomic arrangement itself may be different (reconstruction). These differences affect the surface Debye temperature as well as the detailed processes involved in the adsorption of vapours or other deposited species. Because the electronic wave-functions are discontinued at the free surface, the electrons have energy states at the surface which are not the same as in the bulk. These surface energy states play a tremendously important part in the electronics industry. They also affect the nature of interaction with adsorbed species and this in turn can crucially affect the catalytic activity of the surface, its chemical activity, oxidation and corrosion. Finally, the solid surface has a macroscopic surface energy which is involved in the thermodynamics of wetting and similar processes. It also affects diffusion which is important in the technological problem of sintering. At another level of macroscopic concepts the surface is often a source of flaws or cracks and if the solid is brittle they may play a significant role in the overall strength of the solid. The surface may also contain emergent dislocations: these play a part in crystal growth as well as in the ductile strength of the surface layers. In all these areas there is a great scope for further research and for technological development.

A short bibliography, referred to by numbers in the text, is given at the end. This should be more useful to readers than a long list of references.     

Chemical and electronic properties of sulfur-passivated InAs surfaces

Treatment with ammonium sulfide ((NH₄)₂S_x) solutions is used to produce model passivated InAs(0 0 1) surfaces with well-defined chemical and electronic properties. The passivation effectively removes oxides and contaminants, with minimal surface etching, and creates a covalently bonded sulfur layer with good short-term stability in ambient air and a variety of aqueous solutions, as characterized by X-ray photoelectron spectroscopy, atomic force microscopy, and Hall measurements. The sulfur passivation also preserves the surface charge accumulation layer, increasing the associated downward band bending.     

Structure and electronic properties of oxyanionic crystal surfaces

The atomic and electronic structures of the surfaces of alkali-metal nitrates, chlorates, and perchlorates are determined in the gradient approximation of density functional theory via the linear combination of atomic orbitals using the CRYSTAL09 program package. The geometric parameters, surface energies, densities of states, overlap populations, and atomic charges are calculated. It is established that the upper layer is formed by oxygen atoms for the most stable surfaces. For oxygen atoms of the upper layer, the intra-anionic bond length decreases with respect to that in the bulk, the overlap populations increase, and the charges decrease. Changes in the atomic and electronic structures of the surface decrease with respect to those of the bulk as the cation atomic number increases.     

磁场中碳纳米管电子结构的紧束缚法研究

利用石墨平面碳原子轨道作sp2杂化时π电子的紧束缚模型,对磁场中直状单层碳纳米管(SWNTs)的电子结构进行理论推导和分析。磁场对碳纳米管的波矢产生影响,从而使碳纳米管的电子结构及能隙均以磁通量子Φ0(=h/e)为周期随磁通量Φ周期性变化。     

Electronic and magnetic properties of 3d transition-metal selenides from first principles

We have studied the electronic and magnetic properties of the PbO-type 3d transition-metal selenides (TMSes) by first principles calculations. We find that TiSe and VSe have ionic type bonds and the other TM-Se bonds are the mixed metallic-ionic-covalent type similar to the Fe–As bonds in the iron-based superconductors. FeSe has the shortest TM-Se bond and unique stripe antiferromagnetic ground state. CrSe and MnSe have a ferromagnetic ground state, while the other TMSes have a nonmagnetic ground state. Both nonmagnetic Co dopants and magnetic Mn dopants in FeSe compress the stripe antiferromagnetic state, while the magnetic trends are different as the doping concentration increases.     

Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

The electronic structure and magnetic properties of the transition-metal(TM) atoms(Sc–Zn, Pt and Au) doped zigzag GaN single-walled nanotubes(NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Codoped GaN NTs induce the largest local moment of 4μB among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it.