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Calculates lattice constant of hexagonal bulk structures at zero temperature and pressure by using simplex minimization to minimize the potential energy.

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Indium phosphide is investigated using molecular dynamics (MD) simulations and density-functional theory calculations. MD simulations use a proposed effective interaction potential for InP fitted to a selected experimental dataset of properties. The potential consists of two- and three-body terms that represent atomic-size effects, charge–charge, charge–dipole and dipole–dipole interactions as well as covalent bond bending and stretching. Predictions are made for the elastic constants as a function of density and temperature, the generalized stacking fault energy and the low-index surface energies.

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This is a model driver for an optimized interatomic potential based on a modified Tersoff form originally constructed for bulk silicon and 2D silicon (silicene). The silicon potential reproduces a wide range of properties of Si and improves over existing potentials with respect to point defect structures and energies, surface energies and reconstructions, thermal expansion, melting temperature and other properties.

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Based on the idea that bonding energies of many substances can be modeled by pairwise interactions moderated by the local environment, we propose a new universal interatomic potential for tetrahedrally bonded materials. We obtain two basic relationships linking equilibrium interatomic distances and cohesive energies to the coordination number for a large range of phases of silicon. The relationships are also valid for germanium and carbon, covering, in the latter case, double and triple carbon-carbon bonds, where pi-bonding is important. Based on these ideas we discuss the construction of the universal interatomic potential for these three substances. This potential, which uses very few parameters, should be useful, particularly for surface studies.

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- Software/Code

This is a Cr Morse Model Parameterization by Girifalco and Weizer (1959) using a low-accuracy cutoff distance. The Morse parameters were calculated using experimental values for the energy of vaporization, the lattice constant, and the compressibility. The equation of state and the elastic constants which were computed using the Morse parameters, agreed with experiment for both face-centered and body-centered cubic metals. All stability conditions were also satisfied for both the face-centered and the body-centered metals. This shows that the Morse function can be applied validly to problems involving any type of deformation of the cubic metals.

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- Software/Code

This is a Cr Morse Model Parameterization by Girifalco and Weizer (1959) using a high-accuracy cutoff distance. The Morse parameters were calculated using experimental values for the energy of vaporization, the lattice constant, and the compressibility. The equation of state and the elastic constants which were computed using the Morse parameters, agreed with experiment for both face-centered and body-centered cubic metals. All stability conditions were also satisfied for both the face-centered and the body-centered metals. This shows that the Morse function can be applied validly to problems involving any type of deformation of the cubic metals.

Data Types:

- Software/Code

LAMMPS Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential with Morse long-range interactions for C-H systems ('pair_style airebo/morse' with potential file CH.airebo-m). Abstract: The Adaptive Intermolecular Reactive Empirical Bond Order potential (AIREBO) for hydrocarbons has been widely used to study dynamic bonding processes under ambient conditions. However, its intermolecular interactions are modeled by a Lennard-Jones (LJ) potential whose unphysically divergent power-law repulsion causes AIREBO to fail when applied to systems at high pressure. We present a modified potential, AIREBO-M, where we have replaced the singular Lennard-Jones potential with a Morse potential. We optimize the new functional form to improve intermolecular steric repulsions, while preserving the ambient thermodynamics of the original potentials as much as possible. The potential is fit to experimental measurements of the layer spacing of graphite up to 14 GPa and first principles calculations of steric interactions between small alkanes. To validate AIREBO-M's accuracy and transferability, we apply it to a graphite bilayer and orthorhombic polyethylene. AIREBO-M gives bilayer compression consistent with quantum calculations, and it accurately reproduces the quasistatic and shock compression of orthorhombic polyethlyene up to at least 40 GPa.

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A dropout uncertainty neural network (DUNN) potential for condensed-matter carbon systems with a dropout ratio of 0.3. This is an ensemble model consisting of 100 different network structures obtained by dropout. Before dropout, there are three hidden layers each containing 128 neurons; each neuron in the hidden layers has probability 0.3 of being removed from the network. By default, the model will run in the 'mean' mode where the output energy, forces, and virial are obtained by averaging over the 100 ensembles. If desired, one can set the 'active_member_id' to '0' to use the fully-connected structure or to '1, 2, ..., 100' to use a single ensemble member. When multiple ensemble members are used, the ensemble average of the energy and forces are what are ultimately returned for a given configuration.

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- Software/Code

Effective Medium Theory (EMT) model based on the EMT implementation in ASAP (https://wiki.fysik.dtu.dk/asap). Effective Medium Theory is a many-body potential of the same class as Embedded Atom Method, Finnis-Sinclair etc. The main term in the energy per atom is the local density of atoms. The functional form implemented here is that of Ref. 1. The principles behind EMT are described in Refs. 2 and 3 (with 2 being the more detailed and 3 being the most pedagogical). Be aware that the functional form and even some of the principles have changed since refs 2 and 3. EMT can be considered the last step of a series of approximations starting with Density Functional Theory; see Ref 4. This model implements the "official" parametrization as published in Ref. 1. This parametrization is appropriate for single-element simulations of gold (Au). For alloy simulations, please use the alloy parametrization EMT_Asap_Standard_JacobsenStoltzeNorskov_1996_AlAgAuCuNiPdPt which uses a slightly larger cutoff to accomodate for all the elements, at the price of changing the properties of the individual elements marginally. These files are based on Asap version 3.11.5. REFERENCES: [1] Jacobsen, K. W., Stoltze, P., & Nørskov, J.: "A semi-empirical effective medium theory for metals and alloys". Surf. Sci. 366, 394–402 (1996). [2] Jacobsen, K. W., Nørskov, J., & Puska, M.: "Interatomic interactions in the effective-medium theory". Phys. Rev. B 35, 7423–7442 (1987). [3] Jacobsen, K. W.: "Bonding in Metallic Systems: An Effective-Medium Approach". Comments Cond. Mat. Phys. 14, 129-161 (1988). [4] Chetty, N., Stokbro, K., Jacobsen, K. W., & Nørskov, J.: "Ab initio potential for solids". Phys. Rev. B 46, 3798–3809 (1992). KNOWN ISSUES / BUGS: * On-the-fly modifications of the parameters is not supported, and should be implemented in the future.

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- Software/Code

A set of modified embedded-atom method (MEAM) potentials for the interactions between Al, Si, Mg, Cu, and Fe was developed from a combination of each element's MEAM potential in order to study metal alloying. Previously published MEAM parameters of single elements have been improved for better agreement to the generalized stacking fault energy (GSFE) curves when compared with ab initio generated GSFE curves. The MEAM parameters for element pairs were constructed based on the structural and elastic properties of element pairs in the NaCl reference structure garnered from ab initio calculations, with adjustment to reproduce the ab initio heat of formation of the most stable binary compounds. The new MEAM potentials were validated by comparing the formation energies of defects, equilibrium volumes, elastic moduli, and heat of formation for several binary compounds with ab initio simulations and experiments. Single elements in their ground-state crystal structure were subjected to heating to test the potentials at elevated temperatures. An Al potential was modified to avoid formation of an unphysical solid structure at high temperatures. The thermal expansion coefficient of a compound with the composition of AA 6061 alloy was evaluated and compared with experimental values. MEAM potential tests performed in this work, utilizing the universal atomistic simulation environment (ASE), are distributed to facilitate reproducibility of the results.

Data Types:

- Software/Code