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Citation: H. Gao, A. Otero-de-la-Roza, S.M. Aouadi, E.R. Johnson, and A. Martini (2013), "An empirical model for silver tantalate", Modelling and Simulation in Materials Science and Engineering, 21(5), 55002. DOI: 10.1088/0965-0393/21/5/055002.
Abstract: A set of parameters for the modified embedded atom method (MEAM) potential was developed to describe the perovskite silver tantalate (AgTaO3). First, MEAM parameters for AgO and TaO were determined based on the structural and elastic properties of the materials in a B1 reference structure predicted by density-functional theory (DFT). Then, using the fitted binary parameters, additional potential parameters were adjusted to enable the empirical potential to reproduce DFT-predicted lattice structure, elastic constants, cohesive energy and equation of state for the ternary AgTaO3. Finally, thermal expansion was predicted by a molecular dynamics (MD) simulation using the newly developed potential and compared directly to experimental values. The agreement with known experimental data for AgTaO3 is satisfactory, and confirms that the new empirical model is a good starting point for further MD studies.

LAMMPS pair_style meam (2013--Gao-H--AgTaO3--LAMMPS--ipr2)
Notes: These files were sent by Dr. Ashlie Martini (Univ. California Merced) and approved for distribution on 6 Jul. 2013. The file AgTaO3_40atoms.dat contains atomic coordinates for the 40-atom cell described in the paper. A sample LAMMPS input script to calculate the cohesive energy of that configuration is in in.AgTaO3. This potential was tested on the following versions of LAMMPS: 5Mar12, 12Apr12, 19May12, 4Jul12, 28Oct12, 21Feb13, 5Jun13, 13Jun13, 17Jun13.
File(s):
 
Citation: J. Byggmästar, E.A. Hodille, Y. Ferro, and K. Nordlund (2018), "Analytical bond order potential for simulations of BeO 1D and 2D nanostructures and plasma-surface interactions", Journal of Physics: Condensed Matter, 30(13), 135001. DOI: 10.1088/1361-648x/aaafb3.
Abstract: An analytical interatomic bond order potential for the Be–O system is presented. The potential is fitted and compared to a large database of bulk BeO and point defect properties obtained using density functional theory. Its main applications include simulations of plasma-surface interactions involving oxygen or oxide layers on beryllium, as well as simulations of BeO nanotubes and nanosheets. We apply the potential in a study of oxygen irradiation of Be surfaces, and observe the early stages of an oxide layer forming on the Be surface. Predicted thermal and elastic properties of BeO nanotubes and nanosheets are simulated and compared with published ab initio data.

Notes: J. Byggmästar (University of Helsinki) noted that the pure elemental potentials for Be-Be and O-O are from the following references:
Be-Be: Björkas, C., Juslin, N., Timko, H., Vörtler, K., Nordlund, K., Henriksson, K., & Erhart, P. (2009). Interatomic potentials for the Be–C–H system. Journal of Physics: Condensed Matter, 21(44), 445002. DOI: 10.1088/0953-8984/21/44/445002
O-O: Erhart, P., Juslin, N., Goy, O., Nordlund, K., Müller, R., & Albe, K. (2006). Analytic bond-order potential for atomistic simulations of zinc oxide. Journal of Physics: Condensed Matter, 18(29), 6585–6605. DOI: https://doi.org/10.1088/0953-8984/18/29/003
which should be cited if only the Be-Be or O-O parts are used.

LAMMPS pair_style tersoff/zbl (2018--Byggmastar-J--Be-O--LAMMPS--ipr1)
Notes: These files were sent by J. Byggmästar (University of Helsinki) on 6 Mar. 2018 and posted with his permission.
File(s):
 
Citation: K. Chenoweth, A.C.T. van Duin, and W.A. Goddard (2008), "ReaxFF Reactive Force Field for Molecular Dynamics Simulations of Hydrocarbon Oxidation", The Journal of Physical Chemistry A, 112(5), 1040-1053. DOI: 10.1021/jp709896w.
Abstract: To investigate the initial chemical events associated with high-temperature gas-phase oxidation of hydrocarbons, we have expanded the ReaxFF reactive force field training set to include additional transition states and chemical reactivity of systems relevant to these reactions and optimized the force field parameters against a quantum mechanics (QM)-based training set. To validate the ReaxFF potential obtained after parameter optimization, we performed a range of NVT−MD simulations on various hydrocarbon/O2 systems. From simulations on methane/O2, o-xylene/O2, propene/O2, and benzene/O2 mixtures, we found that ReaxFF obtains the correct reactivity trend (propene > o-xylene > methane > benzene), following the trend in the C−H bond strength in these hydrocarbons. We also tracked in detail the reactions during a complete oxidation of isolated methane, propene, and o-xylene to a CO/CO2/H2O mixture and found that the pathways predicted by ReaxFF are in agreement with chemical intuition and our QM results. We observed that the predominant initiation reaction for oxidation of methane, propene, and o-xylene under fuel lean conditions involved hydrogen abstraction of the methyl hydrogen by molecular oxygen forming hydroperoxyl and hydrocarbon radical species. While under fuel rich conditions with a mixture of these hydrocarbons, we observed different chemistry compared with the oxidation of isolated hydrocarbons including a change in the type of initiation reactions, which involved both decomposition of the hydrocarbon or attack by other radicals in the system. Since ReaxFF is capable of simulating complicated reaction pathways without any preconditioning, we believe that atomistic modeling with ReaxFF provides a useful method for determining the initial events of oxidation of hydrocarbons under extreme conditions and can enhance existing combustion models.

ReaxFF (2008--Chenoweth-K--C-H-O--LAMMPS--ipr1)
Notes: The file "ffield.reax.CHO_2008" was provided by Adri van Duin. From Prof. van Duin: "The ffield-file contains the force field parameters; this file is readable by LAMMPS." The ReaxFF manual (including file formatting information) was obtained from http://www.wag.caltech.edu/home/duin/manual.html. All files were posted with Prof. van Duin's approval. The standalone ReaxFF program is available without charge for academic users by emailing him.
File(s):
 
Citation: P. Broqvist, J. Kullgren, M.J. Wolf, A.C.T. van Duin, and K. Hermansson (2015), "ReaxFF Force-Field for Ceria Bulk, Surfaces, and Nanoparticles", The Journal of Physical Chemistry C, 119(24), 13598-13609. DOI: 10.1021/acs.jpcc.5b01597.
Abstract: We have developed a reactive force-field of the ReaxFF type for stoichiometric ceria (CeO2) and partially reduced ceria (CeO2–x). We describe the parametrization procedure and provide results validating the parameters in terms of their ability to accurately describe the oxygen chemistry of the bulk, extended surfaces, surface steps, and nanoparticles of the material. By comparison with our reference electronic structure method (PBE+U), we find that the stoichiometric bulk and surface systems are well reproduced in terms of bulk modulus, lattice parameters, and surface energies. For the surfaces, step energies on the (111) surface are also well described. Upon reduction, the force-field is able to capture the bulk and surface vacancy formation energies (Evac), and in particular, it reproduces the Evac variation with depth from the (110) and (111) surfaces. The force-field is also able to capture the energy hierarchy of differently shaped stoichiometric nanoparticles (tetrahedra, octahedra, and cubes), and of partially reduced octahedra. For these reasons, we believe that this force-field provides a significant addition to the method repertoire available for simulating redox properties at ceria surfaces.

Notes: J. Kullgren included the following notes: "Usage: The parameters have been tested for static calculations of CeO2 and partially reduced CeO(2-x) using the LAMMPS code with the fortran implementation of reaxFF. For energy comparisons, use the in-cell approach (see the paper) when calculating reaction energies. Note to the users: After publication we have made further use of the published ceria parameters and noticed an additional (false) local minimum occurring for partially reduced ceria at a short Ce-O distance (approx. 1.89 Angstrom). This may (for example) have consequences for dynamic simulations at moderate temperatures. Our attempts to heal this deficiency have so far destroyed the good performance regarding the ordering of the surface vacancy energies on the (111) surface. In relevant cases, we advice our users to analyze the bond distances from the simulations."

ReaxFF (2015--Broqvist-P--Ce-O--LAMMPS--ipr1)
Notes: This file was sent by J. Kullgren (Uppsala University) on 19 December 2016 and posted with his permission.
File(s):
 
Citation: P. Tiwary, A. Walle, B. Jeon, and N. Grønbech-Jensen (2011), "Interatomic potentials for mixed oxide and advanced nuclear fuels", Physical Review B, 83(9), 94104. DOI: 10.1103/physrevb.83.094104.
Abstract: We extend our recently developed interatomic potentials for UO2 to the fuel system (U,Pu,Np)O2. We do so by fitting against an extensive database of ab initio results as well as to experimental measurements. The applicability of these interactions to a variety of mixed environments beyond the fitting domain is also assessed. The employed formalism makes these potentials applicable across all interatomic distances without the need for any ambiguous splining to the well-established short-range Ziegler-Biersack-Littmark universal pair potential. We therefore expect these to be reliable potentials for carrying out damage simulations (and molecular dynamics simulations in general) in nuclear fuels of varying compositions for all relevant atomic collision energies.
Citation: P. Tiwary, A. van de Walle, and N. Grønbech-Jensen (2009), "Ab initio construction of interatomic potentials for uranium dioxide across all interatomic distances", Physical Review B, 80(17), 174302. DOI: 10.1103/physrevb.80.174302.
Abstract: We provide a methodology for generating interatomic potentials for use in classical molecular-dynamics simulations of atomistic phenomena occurring at energy scales ranging from lattice vibrations to crystal defects to high-energy collisions. A rigorous method to objectively determine the shape of an interatomic potential over all length scales is introduced by building upon a charged-ion generalization of the well-known Ziegler-Biersack-Littmark universal potential that provides the short- and long-range limiting behavior of the potential. At intermediate ranges the potential is smoothly adjusted by fitting to ab initio data. Our formalism provides a complete description of the interatomic potentials that can be used at any energy scale, and thus, eliminates the inherent ambiguity of splining different potentials generated to study different kinds of atomic-materials behavior. We exemplify the method by developing rigid-ion potentials for uranium dioxide interactions under conditions ranging from thermodynamic equilibrium to very high atomic-energy collisions relevant for fission events.

GULP
Notes: These files were posted on 17 June 2011 with the approval of Pratyush Tiwary and Axel van de Walle (California Institute of Technology). 30 Jan. 2012 Update: These files are identified as having problems with thermal expansion in UO2 and are superseded by the next GULP implementation below.
File(s): superseded


GULP
Notes: 30 Jan. 2012 Update: These files (version 2.0) were provided by Pratyush Tiwary (California Institute of Technology) and posted with his permission. According to him, this version corrects the "U-U interaction term (truncated at 4 Angstroms) to resolve problems with thermal expansion in UO2." Additional information is located in readme_v2.txt
File(s):
 
Citation: P. Zhang, and D.R. Trinkle (2016), "A modified embedded atom method potential for interstitial oxygen in titanium", Computational Materials Science, 124, 204-210. DOI: 10.1016/j.commatsci.2016.07.039.
Abstract: Modeling oxygen interstitials in titanium requires a new empirical potential. We optimize potential parameters using a fitting database of first-principle oxygen interstitial energies and forces. A new database optimization algorithm based on Bayesian sampling is applied to obtain an optimal potential for a specific testing set of density functional data. A parallel genetic algorithm minimizes the sum of logistic function evaluations of the testing set predictions. We test the transferability of the potential model against oxygen interstitials in HCP titanium, transition barriers between oxygen interstitial sites, and oxygen in the titanium prismatic stacking fault. The potential predicts that the interaction between oxygen and a screw dislocation core is weak and short-ranged.

Notes: Prof. Trinkle said that this potential is specifically intended for dilute oxygen in titanium as there's no oxygen-oxygen interaction. 9 Aug. 2016: the reference information was updated.

LAMMPS pair_style meam/spline (2016--Zhang-P--Ti-O--LAMMPS--ipr1)
Notes: This file was sent by Prof. Dallas Trinkle (Univ. of Illinois) on 6 Aug. 2016 and posted with his permission.
File(s): superseded


LAMMPS pair_style meam/spline (2016--Zhang-P--Ti-O--LAMMPS--ipr2)
Notes: This file was sent by Prof. Dallas Trinkle (Univ. of Illinois) on 9 Aug. 2016 and posted with his permission. This version removes an extra comment line that was not compatible with the LAMMPS MEAM/spline code.
File(s):
 
Citation: A.E. Thompson, B. Meredig, M. Stan, and C. Wolverton (2014), "Interatomic potential for accurate phonons and defects in UO2", Journal of Nuclear Materials, 446(1-3), 155-162. DOI: 10.1016/j.jnucmat.2013.11.040.
Abstract: We have developed an improved uranium dioxide interatomic potential by fitting to forces, energies, and stresses of first principles molecular dynamics calculations via a genetic algorithm approach called Iterative Potential Refinement (IPR). We compare the defect energetics and vibrational properties of the IPR-fit potential with other interatomic potentials, density functional theory calculations, and experimental phonon dispersions. We find that among previously published potentials examined, there is no potential that simultaneously yields accurate defect energetics and accurate vibrational properties. In contrast, our IPR-fit potential produces both accurate defects and the best agreement with the experimental phonon dispersion and phonon density of states. This combination of accurate properties makes this IPR-fit potential useful for simulating UO2 in high temperature, defect-rich environments typical for nuclear fuel. Additionally, we verify that density functional theory with a Hubbard U correction accurately reproduces the experimentally derived UO2 phonon density of states.

GULP
Notes: These parameters were sent by Dr. Alexander Thompson and posted with his approval on 25 Nov. 2014.
Parameters:
O core 1.772816
O shell -3.737358
U core -2.069827
U shell 5.998911
spring
U 115.5906
O 261.0604
buck
U shell O shell 1062.316 0.398196 0.0 0.0 15.0
U shell U shell 183.6 0.420031 0.0 0.0 15.0
buck4
O shell O shell 10402.58 0.238539 81.75059 0.0 1.150671 2.22 2.460169 15.0

Citation: P. Tiwary, A. van de Walle, and N. Grønbech-Jensen (2009), "Ab initio construction of interatomic potentials for uranium dioxide across all interatomic distances", Physical Review B, 80(17), 174302. DOI: 10.1103/physrevb.80.174302.
Abstract: We provide a methodology for generating interatomic potentials for use in classical molecular-dynamics simulations of atomistic phenomena occurring at energy scales ranging from lattice vibrations to crystal defects to high-energy collisions. A rigorous method to objectively determine the shape of an interatomic potential over all length scales is introduced by building upon a charged-ion generalization of the well-known Ziegler-Biersack-Littmark universal potential that provides the short- and long-range limiting behavior of the potential. At intermediate ranges the potential is smoothly adjusted by fitting to ab initio data. Our formalism provides a complete description of the interatomic potentials that can be used at any energy scale, and thus, eliminates the inherent ambiguity of splining different potentials generated to study different kinds of atomic-materials behavior. We exemplify the method by developing rigid-ion potentials for uranium dioxide interactions under conditions ranging from thermodynamic equilibrium to very high atomic-energy collisions relevant for fission events.

Notes: 31 Jan. 2012 Update: This potential has been superseded by the (U,Pu,Np)O2 interatomic potential.

GULP
Notes: These were supplied by Pratyush Tiwary and Axel van de Walle (California Institute of Technology) and posted with their approval on 22 June 2011.
File(s): superseded


Date Created: October 5, 2010 | Last updated: October 05, 2018