Atomistic simulations using interatomic potentials are widely used for analyzing phenomena as diverse as crystal growth and plastic deformation in all classes of materials. The potentials for some material classes, particularly those for metal oxides, are less satisfactory for certain simulations. Many of the potentials currently utilized for metal oxides incorporate a fixed charge ionic component to the interatomic binding. However, these fixed charge potentials incorrectly predict the cohesive energy of ionic materials, and they cannot be used to simulate oxidation at metal surfaces or analyze metal/oxide interfaces where the local ion charge can be significantly different from that in the bulk oxide. A recent charge transfer model proposed by Streitz and Mintmire has in part successfully addressed these issues. However, we find that this charge transfer model becomes unstable at small atomic spacings. As a result, it cannot be used for the studies of energetic processes such as ion bombardment ͑e.g., plasma-assisted vapor deposition͒ where some ions closely approach the others. Additionally, the Streitz-Mintmire charge transfer model cannot be applied to systems involving more than one metal element, precluding study of the oxidation of metal alloys and dissimilar metal oxide/metal oxide interfaces. We have analyzed the origin of these limitations and propose a modified charge transfer model to overcome them. We then unify metal alloy embedded atom method potentials and the modified form of the charge transfer potential to create a general potential that can be used to explore the oxidation of the metallic alloy and the energetic vapor deposition of oxides, and to probe the structure of dissimilar metal oxide/metal oxide or metal alloy/oxide multilayers. Numerical procedures have been developed to efficiently incorporate the potential in molecular dynamics simulations. Several case studies are presented to enable the potential fidelity to be assessed, and an example simulation of the vapor deposition of aluminum oxide is shown to illustrate the potential utility.

Significant differences exist among literature for thermal conductivity of various systems computed using molecular dynamics simulation. In some cases, unphysical results, for example, negative thermal conductivity, have been found. Using GaN as an example case and the direct non-* X. W. Zhou: xzhou@sandia.gov Both the direct and Green-Kubo approaches require long simulations (e.g. at least 1 ns) to reduce the uncertainty due to thermal fluctuations. For the direct method, another difficulty encountered is that the computed thermal conductivity depends strongly on the system length L along the propagation direction, which is typically limited to at most a few hundred nanometers. This means that for perfect bulk crystals the phonon mean free path is comparable to the system size and transport occurs in a partially ballistic regime [17,18,[21][22][23]. It follows from kinetic theory that the computed values of κ are smaller than that of a true bulk system. To obtain values that can be meaningfully compared with experiments, it is therefore necessary to perform several simulations for different cell lengths, and then

CdTe and Cd 1-x Zn x Te are the leading semiconductor compounds for both photovoltaic and radiation detection applications. The performance of these materials is sensitive to the presence of atomic-scale defects in the structures. To enable accurate studies of these defects using modern atomistic simulation technologies, we have developed a high-fidelity analytical bond-order potential for the CdTe system. This potential incorporates primary (σ) and secondary (π) bonding and the valence dependence of the heteroatom interactions. The functional forms of the potential are directly derived from quantum-mechanical tight-binding theory under the condition that the first two and first four levels of the expanded Green's function for the σ-and π-bond orders, respectively, are retained. The potential parameters are optimized using iteration cycles that include first-fitting properties of a variety of elemental and compound configurations (with coordination varying from 1 to 12) including small clusters, bulk lattices, defects, and surfaces, and then checking crystalline growth through vapor deposition simulations. It is demonstrated that this CdTe bond-order potential gives 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 of the CdTe compound. Most importantly, this potential captures the crystalline growth of the ground-state structures for Cd, Te, and CdTe phases in vapor deposition simulations.

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Pressure overcomes balanced particle interactions and enables fine-tuning of nanoparticle lattice, forming new luminescent nanowires.

Palladium hydrides have important applications. However, the complex Pd–H alloy system presents a formidable challenge to developing accurate computational models. In particular, the separation of a Pd–H system to dilute (α) and concentrated (β) phases is a central phenomenon, but the capability of interatomic potentials to display this phase miscibility gap has been lacking. We have extended an existing palladium embedded-atom method potential to construct a new Pd–H embedded-atom method potential by normalizing the elemental embedding energy and electron density functions. The developed Pd–H potential reasonably well predicts the lattice constants, cohesive energies, and elastic constants for palladium, hydrogen, and PdHx phases with a variety of compositions. It ensures the correct hydrogen interstitial sites within the hydrides and predicts the phase miscibility gap. Preliminary molecular dynamics simulations using this potential show the correct phase stability, hydrogen diffusion mechanism, and mechanical response of the Pd–H system.

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