Wangyu Hu

First-principles study of structural, electronic, and multiferroic properties in BiCoO3.

Electronic and magnetic properties of BiCoO(3) have been investigated using the ab initio density-functional calculations with local spin density approximation (LSDA) and LSDA+U methods. The structural stability and the origin of the multiferroism for ferroelectronic and ferromagnetic existence were addressed. It was shown that the stability of the C-type antiferromagnetic (C-AFM) structure is better than that of other possible configurations. The hybridization between Bi-O and Co-O with interplay and a local magnetic moment on the Co(3+) play important roles for the nature of the ferroelectricity and ferromagnetism. Theoretical calculations predict the insulating ground state with a band gap of 2.11 eV in the C-AFM ordering for BiCoO(3) originated from the antiferromagnetic interaction in the ab plane, which is in well agreement with experiments.

Modified analytic EAM potentials for the binary immiscible alloy systems

Abstract Modified analytic embedded atom method (MAEAM) type potentials have been constructed for seven binary immiscible alloy systems: Al–Pb, Ag–Ni, Fe–Cu, Ag–Cu, Cu–Ta, Cu–W and Cu–Co. The potentials are fitted to the lattice constant, cohesive energy, unrelaxed monovacancy formation energy and elastic constants for only pure metals which consist the immiscible alloy systems. In order to test the reliability of the constructed MAEAM potentials, formation enthalpies of disordered alloys for those seven binary immiscible alloy systems have been calculated. The calculated results are in general agreement with the experimental data available and those theoretical results calculated by other authors. As only very limited experimental information is available for alloy properties in immiscible alloy systems, the MAEAM is demonstrated to be a reasonable method to construct the interatomic potentials for immiscible alloy systems because only the properties of pure elements are needed in calculation.

Melting temperature of Pb nanostructural materials from free energy calculation

The thermodynamic properties of lead, including the entropy, heat capacity, Gibbs free energy, and surface free energy have been studied. Based on bulk thermodynamic properties of lead, Gibbs free energy for nanostructural materials is obtained and used to calculate the size-dependent melting point depression for lead nanostructural materials. The studies indicate that the surface free energy difference between solid phase and liquid phase is a decisive factor for the size-dependent melting of nanostructural materials. The calculated results are in agreement with recent experimental values and the available molecular dynamics simulation data.

Embedded-atom-method interatomic potentials from lattice inversion

The present work develops a physically reliable procedure for building the embedded-atom-method (EAM) interatomic potentials for the metals with fcc, bcc and hcp structures. This is mainly based on Chen-Möbius lattice inversion (Chen et al 1997 Phys. Rev. E 55 R5) and first-principles calculations. Following Baskes (Baskes et al 2007 Phys. Rev. B 75 094113), this new version of the EAM eliminates all of the prior arbitrary choices in the determination of the atomic electron density and pair potential functions. Parameterizing the universal form deduced from the calculations within the density-functional scheme for homogeneous electron gas as the embedding function, the new-type EAM potentials for Cu, Fe and Ti metals have successfully been constructed by considering interatomic interactions up to the fifth neighbor, the third neighbor and the seventh neighbor, respectively. The predictions of elastic constants, structural energy difference, vacancy formation energy and migration energy, activation energy of vacancy diffusion, latent heat of melting and relative volume change on melting all satisfactorily agree with the experimental results available or first-principles calculations. The predicted surface energies for low-index crystal faces and the melting point are in agreement with the experimental data to the same extent as those calculated by other EAM-type potentials such as the FBD-EAM, 2NN MEAM and MS-EAM. In addition, the order among the predicted low-index surface energies is also consistent with the experimental information.

The dynamic diffusion behaviors of 2D small Fe clusters on a Fe(110) surface

In this paper, the diffusion behaviors of Fe clusters on a Fe(110) surface have been investigated using molecular dynamics simulations based on a modified analytic embedded-atom method. The stable configurations of Fe clusters are predicted to be close-packed islands configuration for Fe clusters up to nine atoms or even larger in size. The activation energy of surface diffusion exhibits an interesting, oscillatory behavior as a function of cluster size. As compared to the structures with extra atoms at the periphery, compact geometric configurations of Fe clusters (four- and seven-atom clusters) have an obviously higher activation energy. The reason is that for clusters of more than two atoms the diffusion mechanisms of 2D small clusters are achieved by the migration of extra atoms at the periphery.

Temperature effects on growth configurations of Al atoms on an Fe rhombohedron: a molecular dynamics simulation

The growth of Al atoms on an Fe rhombohedral nanoparticle with 1,105 atoms in the temperature range of 100–1,200xa0K is studied by molecular dynamics and embedded atom method. Several thermodynamics parameters, including potential energy, radial distribution function, and Lindemann index are used for the growth process analysis. This study reports an increasing energy per Fe atom and a decreasing energy per Al atom with increasing temperature. Alloying between Fe and Al atoms accelerates at higher temperatures, because of the incorporation of more Al atoms into the Fe core. Three different growth configurations are found for the simulations at different temperatures. At temperatures below 800 K, the core–shell configuration with Fe and Al as core and shell, respectively, is the most favorable. At approximately 800 K, a nanoparticle with surface alloying order is formed. Finally, surface melting occurs at growth temperatures higher than 900 K.

Surface self-diffusion behavior of individual tungsten adatoms on rhombohedral clusters

The diffusion of single tungsten adatoms on the surfaces of rhombohedral clusters is studied by means of molecular dynamics and the embedded atom method. The energy barriers for the adatom diffusing across and along the step edge between a {110} facet and a neighboring {110} facet are calculated using the nudged elastic band method. We notice that the tungsten adatom diffusion across the step edge has a much higher barrier than that for face-centered cubic metal clusters. The result shows that diffusion from the {110} facet to a neighboring {110} facet could not take place at low temperatures. In addition, the calculated energy barrier for an adatom diffusing along the step edge is lower than that for an adatom on the flat (110) surface. The results show that the adatom could diffuse easily along the step edge, and could be trapped by the facet corner. Taking all of this evidence together, we infer that the {110} facet starts to grow from the facet corner, and then along the step edge, and finally toward the {110} facet center. So the tungsten rhombohedron can grow epitaxially along the {110} facet one facet at a time and the rhombohedron should be the stable structure for both large and small tungsten clusters.