Chen Nan-Xian

Phase stability and site preference of Sm(Fe,T)12

Abstract The structure of intermetallics Sm(Fe,T) 12 is analyzed via a quasi-ab initio pair potentials Φ Fe–Fe ( r ), Φ Sm–Fe ( r ), Φ Sm–Sm ( r ), Φ Sm–T ( r ), Φ Fe–T ( r ) and Φ T–T ( r ). The calculation results show that each of Cr, V, Mo and Ti significantly decreases the cohesive energy of Sm(Fe,T) 12 , and thus stabilizes its structure of ThMn 12 . The calculated lattice constants coincide quite well with experimental values. The sequence of site preference occupation is 8i, 8j and 8f, with the 8i occupation corresponding to the greatest energy decrease. The calculated results also show that each of Co, Cu, Ni and Sc does not stabilize the system with the structure of ThMn 12 . The calculated crystal structure can recover after either an overall wide-range macro-deformation or atomic random motion, demonstrating that an Sm–Fe–T system has the stable structure of ThMn 12 . The crystal space group remaining consistent at different temperatures is also shown in this paper. All of the results verify that the first principle potentials based on the lattice inversion technique are effective.

Site preference and vibrational properties of ScFexAl12−x

Abstract The site preference of Fe in ScFe x Al 12− x is studied using the interatomic potentials. These potentials between the identical and distinct atoms are obtained by a strict lattice inversion method. The lattice constants of ScFe x Al 12− x with different x are calculated, which are in good agreement with the experiments. This work presents the phonon densities of states of these ternary intermetallic compounds with ThMn 12 -type structure. A qualitative analysis is carried out with the relevant potentials for the vibrational modes, which makes it possible to predict some properties related to lattice vibration.

Chen's lattice inversion embedded-atom method for Ni?Al alloy

The structural properties, the enthalpies of formation, and the mechanical properties of some Ni–Al intermetallic compounds (NiAl, Ni3Al, NiAl3, Ni5Al3, Ni3Al4) are studied by using Chen’s lattice inversion embedded-atom method (CLI-EAM). Our calculated lattice parameters and cohesive energies of Ni–Al compounds are consistent with the experimental and the other EAM results. The results of enthalpy of formation indicate a strong chemical interaction between Ni and Al in the intermetallic compounds. Through analyzing the alloy elastic constants, we find that all the Ni–Al intermetallic compounds discussed are mechanically stable. The bulk moduli of the compounds increase with the increasing Ni concentration. Our results also suggest that NiAl, Ni3Al, NiAl3, and Ni5Al3 are ductile materials with lower ratios of shear modulus to bulk modulus; while Ni3Al4 is brittle with a higher ratio.

Lattice-Inversion Embedded-Atom-Method Interatomic Potentials for Group-VA Transition Metals

The lattice-inversion embedded-atom-method (LI-EAM) interatomic potential we developed previously [J. Phys.: Condens. Matter 22 (2010) 375503] is extended to group-VA transition metals (V, Nb and Ta). It is found that considering interatomic interactions up to appropriate-distance-neighbor atoms is crucial to constructing accurate EAM potentials, especially for the prediction of surface energy. The LI-EAM interatomic potentials for group-VA transition metals are successfully built by considering interatomic interactions up to the fifth neighbor atoms. These angular-independent potentials drastically promote the accuracy of the predicted surface energies, which match the experimental results well.

Statistical Average of Spin Operators for Calculation of Three-Component Magnetization (II): Solution of Equation

In this paper, the solution of Chebyshev equation with its argument being greater than 1 is obtained. The initial value of the derivative of the solution is the expression of magnetization, which is valid for any spin quantum number S. The Chebyshev equation is transformed from an ordinary differential equation obtained when we dealt with Heisenberg model, in order to calculate all three components of magnetization, by many-body Greens function under random phase approximation. The Chebyshev functions with argument being greater than 1 are discussed. This paper shows that the Chebyshev polynomials with their argument being greater than 1 have their physical application.

Statistical Average of Spin Operators for Calculation of Three-Component Magnetization

When one wants to calculate all the three components of magnetization of Heisenberg model under random phase approximation, at least one of the components should be the solution of an ordinary differential equation. In this paper such an equation is established. It is argued that the general expressions of magnetization for any spin quantum number S suggested before are the solution of the ordinary differential equation.

Monte Carlo simulation of the reorientation transition in Heisenberg model with dipole interactions

The change of magnetic states in ultrathin films with temperature have been simulated by Monte Carlo method. A Heisenberg model with long-range dipole interactions was adopted in our calculations. The results were qualitatively in good agreement with the experimental phenomena. That is at low temperatures the magnetization is perpendicular to the plane, and at higher temperatures but below the Curie point, the magnetization is mostly within the plane. In between these two regions, the magnetization seems to be suppressed. The simulations show that the loss of magnetization is a consequence of the special magnetic states in which the local domains orientations are reverse with the neighbor ones.

Interfacial potential approach for Ag/ZnO (0001) interfaces

Systematic approaches are presented to extract the interfacial potentials from the ab initio adhesive energy of the interface system by using the Chen—Mobius inversion method. We focus on the interface structure of the metal (111)/ZnO (0001) in this work. The interfacial potentials of Ag—Zn and Ag—O are obtained. These potentials can be used to solve some problems about Ag/ZnO interfacial structure. Three metastable interfacial structures are investigated in order to check these potentials. Using the interfacial potentials we study the procedure of interface fracture in the Ag/ZnO (0001) interface and discuss the change of the energy, stress, and atomic structures in tensile process. The result indicates that the exact misfit dislocation reduces the total energy and softens the fracture process. Meanwhile, the formation and mobility of the vacancy near the interface are observed.

Construction of embedded-atom-method interatomic potentials for alkaline metals (Li, Na, and K) by lattice inversion

The lattice-inversion embedded-atom-method interatomic potential developed previously by us is extended to alkaline metals including Li, Na, and K. It is found that considering interatomic interactions between neighboring atoms of an appropriate distance is a matter of great significance in constructing accurate embedded-atom-method interatomic potentials, especially for the prediction of surface energy. The lattice-inversion embedded-atom-method interatomic potentials for Li, Na, and K are successfully constructed by taking the fourth-neighbor atoms into consideration. These angular-independent potentials markedly promote the accuracy of predicted surface energies, which agree well with experimental results. In addition, the predicted structural stability, elastic constants, formation and migration energies of vacancy, and activation energy of vacancy diffusion are in good agreement with available experimental data and first-principles calculations, and the equilibrium condition is satisfied.

Tuning of the periodicity of stable self-organized metallic templates＊

The atomic and electronic structures of Pb bilayer/Pt(111) are investigated with two theoretical calculations. We find that the stable (2 × 2)/(3 × 3) Pb/Pt(111) structure is a promising candidate for being used as a template with self-organized ordered Pb semi-cluster array on the first Pb monolayer. This stable structure can realize the ordered Au single-atom array around the Pb semi-clusters that can cause selective adsorption of noble atoms. The size of Pb magic number semi-cluster plays a more important role in determining the periodicity of the template than the lattice constant misfit between the substrate and the overlayer. This leads to quite a different periodicity between the two stable templates, which are (2 × 2)/(3 × 3) Pb/Pt(111) and Pb/Cu(111). Therefore, by considering the size of the stable semi-clusters and carefully selecting different substrate materials, we can tune the density of Pb semi-clusters as the nucleation points and then tune the periodicity of the stable template.