Abstract: Interatomic potentials for pure Zn and Mg-Zn binary system have been developed on the basis of the second nearest-neighbor modified embedded-atom method formalism. The potentials describe fundamental material properties of pure Zn (bulk, defect, and thermal properties) reasonably and reproduce the alloy behavior (thermodynamic, structural, and elastic properties of compounds and solution phases) of Mg-Zn alloys well in good agreement with experiments, first-principles and CALPHAD. The applicability of the developed potentials to atom-scale investigations on the slip behavior of Mg-Zn alloys is also demonstrated by showing that the calculated effects of Zn on the general stacking fault energy on the basal, prismatic and pyramidal planes are consistent with first-principles calculations.

Abstract: Because of its very large c/a ratio, zinc has proven to be a difficult element to model using semi-empirical classical potentials. It has been shown, in particular, that for the modified embedded atom method (MEAM), a potential cannot simultaneously have an hcp ground state and c/a ratio greater than ideal. As an alloying element, however, useful zinc potentials can be generated by relaxing the condition that hcp be the lowest energy structure. In this paper, we present a MEAM zinc potential, which gives accurate material properties for the pure state, as well as a MEAM ternary potential for the Mg-Al-Zn system which will allow the atomistic modeling of a wide class of alloys containing zinc. The effects of zinc in simple Mg-Zn for this potential is demonstrated and these results verify the accuracy for the new potential in these systems.

Abstract: Mg–Zn–Ca alloys are representative Mg alloys with high formability at room temperature. Their high formability is thought to be related to slip, twinning, and recrystallization of the alloys, but the detailed mechanisms have not yet been clarified. To enable atomistic simulations for investigating those behaviors, an interatomic potential for the Mg–Zn–Ca ternary system was developed. The development was based on the second nearest-neighbor modified embedded-atom method formalism, combining previously developed Mg–Zn and Mg–Ca potentials with the newly developed Zn–Ca binary potential. The Zn–Ca and Mg–Zn–Ca potentials reproduce structural, elastic, and thermodynamic properties of compounds and solution phases of relevant alloy systems in reasonable agreement with experimental data, first-principles and CALPHAD calculations. The applicability of the developed potentials is demonstrated through calculations of the effects of Zn and Ca solutes on the generalized stacking fault energy for various slip systems, segregation energy on twin boundaries, and volumetric misfit strain.

Abstract: Bulk and multilayered thin film crystals of II-VI semiconductor compounds are the leading materials for infrared sensing, γ-ray detection, photovoltaics, and quantum dot lighting applications. The key to achieving high performance for these applications is reducing crystallographic defects. Unfortunately, past efforts to improve these materials have been prolonged due to a lack of understanding with regards to defect formation and evolution mechanisms. To enable high-fidelity and high-efficiency atomistic simulations of defect mechanisms, this paper develops a Stillinger-Weber interatomic potential database for semiconductor compounds composed of the major II-VI elements Zn, Cd, Hg, S, Se, and Te. The potential's fidelity is achieved by optimizing all the pertinent model parameters, by imposing reasonable energy trends to correctly capture the transformation between elemental, solid solution, and compound phases, and by capturing exactly the experimental cohesive energies, lattice constants, and bulk moduli of all binary compounds. Verification tests indicate that our model correctly predicts crystalline growth of all binary compounds during molecular dynamics simulations of vapor deposition. Two stringent cases convincingly show that our potential is applicable for a variety of compound configurations involving all the six elements considered here. In the first case, we demonstrate a successful molecular dynamics simulation of crystalline growth of an alloyed (Cd0.28Zn0.68Hg0.04) (Te0.20Se0.18S0.62) compound on a ZnS substrate. In the second case, we demonstrate the predictive power of our model on defects, such as misfit dislocations, stacking faults, and subgrain nucleation, using a complex growth simulation of ZnS/CdSe/HgTe multilayers that also contain all the six elements considered here. Using CdTe as a case study, a comprehensive comparison of our potential with literature potentials is also made. Finally, we also propose unique insights for improving the Stillinger-Weber potential in future developments.

Abstract: This paper reports an updated parameterization for a CdTe bond order potential. The original potential is a rigorously parameterized analytical bond order potential for ternary the Cd–Zn–Te systems. This potential effectively captures property trends of multiple Cd, Zn, Te, CdZn, CdTe, ZnTe, and Cd_1-xZn_xTe phases including clusters, lattices, defects, and surfaces. It also enables crystalline growth simulations of stoichiometric compounds/alloys from non-stoichiometric vapors. However, the potential over predicts the zinc-blende CdTe lattice constant compared to experimental data. Here, we report a refined analytical Cd–Zn–Te bond order potential parameterization that predicts a better CdTe lattice constant. Characteristics of the second potential are given based on comparisons with both literature potentials and the quantum mechanical calculations.

Abstract: Cd-Zn-Te ternary alloyed semiconductor compounds are key materials in radiation detection and photovoltaic applications. Currently, crystalline defects such as dislocations limit the performance of these materials. Atomistic simulations are a powerful method for exploring crystalline defects at a resolution unattainable by experimental techniques. To enable accurate atomistic simulations of defects in the Cd-Zn-Te systems, we develop a full Cd-Zn-Te ternary bond-order potential. This Cd-Zn-Te potential has numerous unique advantages over other potential formulations: (1) It is analytically derived from quantum mechanical theories and is therefore more likely to be transferable to environments that are not explicitly tested. (2) A variety of elemental and compound configurations (with coordination varying from 1 to 12) including small clusters, bulk lattices, defects, and surfaces are explicitly considered during parameterization. As a result, the potential captures structural and property trends close to those seen in experiments and quantum mechanical calculations and provides a good description of melting temperature, defect characteristics, and surface reconstructions. (3) Most importantly, this potential is validated to correctly predict the crystalline growth of the ground-state structures for Cd, Zn, Te elements as well as CdTe, ZnTe, and Cd_1−xZn_xTe compounds during highly challenging molecular dynamics vapor deposition simulations.

Abstract: An embedded atom method potential has been developed for copper–zinc alloys valid from 0% to 37% zinc content (dedicated to describe the α fcc phase). It has been fit to a set of first-principles data for the fcc copper, the fcc Cu₃Zn DO₂₃ phase and Zn on a fcc lattice. Elastic anisotropies, the lattice parameter, cohesive energy are used as input. Ponctual defects, surface energies, intrinsic stacking fault and phonon spectrum have been computed and compare well with experimental trends. This potential has been used to study dislocation dissociation and dislocation emission at a crack tip up to 30% Zn. Dislocation emission at the crack tip is correctly described compared with recent parametrization including the surface energy. It is found that with alloying, dislocation emission becomes easier following the decrease of the unstable stacking fault energy with Zn concentration, a non-trivial finding. This potential is therefore well suited to carry out basic studies of plasticity and fracture in α-brass alloys.

Abstract: Interatomic potentials for pure Zn and Mg-Zn binary system have been developed on the basis of the second nearest-neighbor modified embedded-atom method formalism. The potentials describe fundamental material properties of pure Zn (bulk, defect, and thermal properties) reasonably and reproduce the alloy behavior (thermodynamic, structural, and elastic properties of compounds and solution phases) of Mg-Zn alloys well in good agreement with experiments, first-principles and CALPHAD. The applicability of the developed potentials to atom-scale investigations on the slip behavior of Mg-Zn alloys is also demonstrated by showing that the calculated effects of Zn on the general stacking fault energy on the basal, prismatic and pyramidal planes are consistent with first-principles calculations.

Abstract: We present here simulation results on the dynamical structure factor of the C14 Laves Phase of MgZn₂, the simplest of the Mg–(Al,Zn) Frank-Kasper alloy phases. The dynamical structure factor was determined in two ways. Firstly, the dynamical matrix was obtained in harmonic approximation from ab-initio forces. The dynamical structure factor can then be computed from the eigenvalues of the dynamical matrix. Alternatively, Molecular Dynamics simulations of a larger sample were used to measure the correlation function corresponding to the dynamical structure factor. Both results are compared to data from neutron scattering experiments. This comparison also includes the intensity distribution, which is a very sensitive test. We find that the dynamical structure factor determined with either method agrees reasonably well with the experiment. In particular, the intensity transfer from acoustic to optic phonon modes can be reproduced correctly. This shows that simulation studies can complement phonon dispersion measurements.

Abstract: An interatomic potential for zinc oxide and its elemental constituents is derived based on an analytical bond-order formalism. The model potential provides a good description of the bulk properties of various solid structures of zinc oxide including cohesive energies, lattice parameters, and elastic constants. For the pure elements zinc and oxygen the energetics and structural parameters of a variety of bulk phases and in the case of oxygen also molecular structures are reproduced. The dependence of thermal and point defect properties on the cutoff parameters is discussed. As exemplary applications the irradiation of bulk zinc oxide and the elastic response of individual nanorods are studied.