arXiv subjects

X. G. Gong

Publications and source records attributed to X. G. Gong.

48 records · Page 3Linked to original sources

arXiv2007

Magnetism of 3d transition metal atom on Au(110)-(1x2) and Au(111) surfaces

We calculate the magnetism of 3d transition metals on Au(110)-(1$\times$2) surface and Au(111) surface based on the Density Functional Theory. Our results show that the spin moments of the two-side elements of the 3d group such as Ti, V, Co and Ni decrease greater values than those of the middle elements such as Cr and Mn when they absorb on the surfaces. Our results also show the orbital moments of the left-end elements Ti and V increase if they relax together with surface and decrease for the left-end elements such as Co and Ni. The absorbed 3d atoms in the middle of this group still keep the large spin moment similar to their individual atoms due to the strong electronic correlation. PACS: 75.70.Ak, 75.70.Rf, 75.75.+a, 71.15.Mb

cond-mat.mtrl-sci↗

arXiv2007

Magnetism of One-Dimensional Ni monoatomic chain on Au(110)-(1x2) surface

Based on Density Functional Theory with no-collinear-magnetism formulations, we have calculated magnetic anisotropy of supported Ni chains. Our results indicate that the magnetic anisotropy is closely related to orbital quenching. The easiest magnetized axis changes from parallel to perpendicular to the Ni chains once they absorb on the surface. Our results for single absorbed 3d transition metal atom show that the surface relaxation enhances the orbital moments of left-end elements (Ti,V) and quenches the orbital moments of right-end elements (Fe,Co,Ni) on the Au(110)-(1$\times$2) surface. This is because Ti and V atom raise their position above the trough and Fe, Co, Ni atom trap more deeply in the trough after the surface relaxation.

cond-mat.mtrl-sci↗

arXiv2007

Composition and reactivity on Pd/Au(111) surface: A first-principle study

Atomic configurations of two or three Pd substituents on the Au(111) surface are investigated using the first-principles pseudopotential plane wave approach. Pd atoms are found to form second neighborhoods on PdAu(111). The Pd-d band becomes narrow and well below the Fermi level, very different from those in a Pd film or bulk Pd. Nevertheless, surface Pd atoms are still active and serve as independent attractive centers towards adsorbates. The special ensembles are important for catalysis applications because of their ability to confine reactants in a small region.

cond-mat.mtrl-sci↗

arXiv2005

Effects of Al Addition on the Native Defects in Hafnia

Two occupied native defect bands are detected in pure HfO2, with one located in the middle of the band gap and the other slightly above the valence band maximum. The investigation on the electronic structures of hafnium aluminate thin films as a function of Al concentration discloses the evolution of such bands while the density of states of the former one reduces drastically with the Al addition, that of the later one remains rather unaffected. Our first principles studies of the system attribute the two bands to the charged oxygen vacancy, and the oxygen interstitial related defect states of the HfO2, respectively. We further demonstrate that the observed evolution of the defect bands originates from the interaction in-between the added Al and the native defects of pure HfO2, which effectively passivates the VO+ induced mid-gap states but has little effect on other aspects of the electronic structure of the material.

cond-mat.mtrl-sci↗

arXiv2005

The superheated Melting of Grain Boundary

Based on a model of the melting of Grain Boundary (GB), we discuss the possibility of the existence of superheated GB state. A Molecular Dynamics simulation presented here shows that the superheated GB state can realized in the high symmetric tilt GB. Whether the sizes of liquid nuclei exceed a critical size determined the superheating grain boundary melting or not. Our results also indicate that the increase of melting point due to pressure is smaller than the superheating due to nucleation mechanism.

cond-mat.mtrl-sci↗

arXiv2005

Band structure model of magnetic coupling in semiconductors

We present a unified band structure model to explain magnetic ordering in Mn-doped semiconductors. This model is based on the $p$-$d$ and $d$-$d$ level repulsions between the Mn ions and host elements and can successfully explain magnetic ordering observed in all Mn doped II-VI and III-V semiconductors such as CdTe, GaAs, ZnO, and GaN. This model, therefore, provides a simple guideline for future band structure engineering of magnetic semiconductors.

cond-mat.mtrl-sci↗

arXiv2005

Adsorption, Segregation and Magnetization of a Single Mn Adatom on the GaAs (110) Surface

Density functional calculations with a large unit cell have been conducted to investigate adsorption, segregation and magnetization of Mn monomer on GaAs(110). The Mn adatom is rather mobile along the trench on GaAs(110), with an energy barrier of 0.56 eV. The energy barrier for segregation across the trenches is nevertheless very high, 1.67 eV. The plots of density of states display a wide gap in the majority spin channel, but show plenty of metal-induced gap states in the minority spin channel. The Mn atoms might be invisibl in scanning tunneling microscope (STM) images taken with small biases, due to the directional p-d hybridization. For example, one will more likely see two bright spots on Mn/GaAs(110), despite the fact that there is only one Mn adatom in the system.

cond-mat.stat-mech↗

arXiv2004

Monte Carlo Simulation of Surface De-alloying of Au/Ni(110)

Based on BFS model and using Monte Carlo simulation we confirms the de-alloying in immiscible Au/Ni(110) system, and the critical Au coverage when de-alloying happens is also consistent with experiments. At the same time our simulation show that the structural phase transition will lead to the saturation of the number of alloying Au atoms.

cond-mat.mtrl-sci↗

arXiv2001

A new constant-pressure molecular dynamics method for finite system

In this letter, by writing the volume as a function of coordinates of atoms, we present a new constant-pressure molecular dynamics method with parameters free. This method is specially appropriate for the finite system in which the periodic boundary condition does not exist. Simulations on the carbon nanotube and the Ni nanoparticle clearly demonstrate the validity of the method. By using this method, one can easily obtain the equation of states for the finite system under the external pressure.

cond-mat.mtrl-sci↗

arXiv1996

Relationship Between Structural Fractal and Possible Dynamic Scaling Properties in Protein Folding

In this letter, the possible dynamic scaling properties of protein molecules in folding are investigated theoretically by assuming that the protein molecules are percolated networks. It is shown that the fractal character and the fractal dimensionality may exist only for short sequences in large protein molecules and small protein molecules with homogeneous structure, the fractal dimensionality are obtained for different structures. We then show that there might exist the dynamic scaling properties in protein folding, the critical exponents in the folding for some small global proteins with homogeneous structure are obtained. The dynamic critical exponents of the global proteins in folding are relevant to the fractal dimensionality of its structure, which implies the close relationship between the dynamic process in protein folding and its structure kinematics.

cond-mat↗

arXiv1996

Transport and magnetic properties in ferromagnetic manganese-oxide thin films

The transport and magnetic properties in ferromagnetic manganese-oxide thin films are studied based on the model of the coupling between the mobile d-electrons and the core spins in Mn ions. The spontaneous magnetization and the resistivity are obtained for various magnetic fields and temperature. The resistivity in absence of magnetic field and the magnetoresistance exhibit maxima near the Curie temperature, the applied magnetic field moves the position of the resistivity peak to high temperature and suppresses the peak value, which agree with the experimental results. The Hall resistivity is predicted to exhibit maximum near the Curie point. The pressure effect of the magnetoresistance can also be explained qualitatively in this mechanism. The colossal magnetoresistance in ferromagnetic manganese-oxide thin films is attributed to the spin-correlation fluctuation scattering and the low dimensional effect.

cond-mat↗

arXiv1996

Local Magnetic Moments in Nanoscale Systems

The formation of local magnetic moments and its size effect in one- and three-dimension finite systems with magnetic impurity are investigated based on the Anderson hybridizing model in real space. By the exact diagonalization within the self-consistent mean field approximation, it is found that as contrast to that in infinite system, the formation of the local magnetic moment in finite system may strongly depend on the size of system up to a few nanometers. The spectral densities of the local electronic states and the spatial distribution of the magnetic moments for the conduction electrons polarized by the local moment are also obtained. The condition for the occurrence of local magnetic moments in such small systems is discussed. The strong size-dependence of the local magnetic moments in finite system is attributed to the quantum size effect.

cond-mat↗