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Citation: G.P. Purja Pun, K.A. Darling, L.J. Kecskes, and Y. Mishin (2015), "Angular-dependent interatomic potential for the Cu-Ta system and its application to structural stability of nano-crystalline alloys", Acta Materialia, 100, 377-391. DOI: 10.1016/j.actamat.2015.08.052.
Abstract: Atomistic computer simulations are capable of providing insights into physical mechanisms responsible for the extraordinary structural stability and strength of immiscible Cu–Ta alloys. To enable reliable simulations of these alloys, we have developed an angular-dependent potential (ADP) for the Cu–Ta system by fitting to a large database of first-principles and experimental data. This, in turn, required the development of a new ADP potential for elemental Ta, which accurately reproduces a wide range of properties of Ta and is transferable to severely deformed states and diverse atomic environments. The new Cu–Ta potential is applied for studying the kinetics of grain growth in nano-crystalline Cu–Ta alloys with different chemical compositions. Ta atoms form nanometer-scale clusters preferentially located at grain boundaries (GBs) and triple junctions. These clusters pin some of the GBs in place and cause a drastic decrease in grain growth by the Zener pinning mechanism. The results of the simulations are well consistent with experimental observations and suggest possible mechanisms of the stabilization effect of Ta.

Notes: This potential is meant to supplant the Hahibon 2008 Cu-Ta ADP potential by providing a refit of the Ta-Ta and Cu-Ta interactions.

LAMMPS pair_style adp (2015--Purja-Pun-G-P--Cu-Ta--LAMMPS--ipr1)
Notes: The file was provided by Yuri Mishin (George Mason University) on 11 Sep. 2015.
Citation: A. Hashibon, A.Y. Lozovoi, Y. Mishin, C. Elsässer, and P. Gumbsch (2008), "Interatomic potential for the Cu-Ta system and its application to surface wetting and dewetting", Physical Review B, 77(9), 94131. DOI: 10.1103/physrevb.77.094131.
Abstract: An angle-dependent interatomic potential has been developed for the Cu-Ta system by crossing two existing potentials for pure Cu and Ta. The cross-interaction functions have been fitted to first-principles data generated in this work. The potential has been extensively tested against first-principles energies not included in the fitting database and applied to molecular dynamics simulations of wetting and dewetting of Cu on Ta. We find that a Cu film placed on a Ta (110) surface dewets from it, forming a Cu droplet on top of a stable Cu monolayer. We also observe that a drop of liquid Cu placed on a clean Ta (110) surface spreads over it as a stable monolayer, while the extra Cu atoms remain in the drop. The stability of a Cu monolayer and instability of thicker Cu films are consistent with recent experiments and first-principles calculations. This agreement demonstrates the utility of the potential for atomistic simulations of Cu-Ta interfaces.

Notes: Prof. Mishin requested the following be noted: There was a typing error in the original ADP paper (Y. Mishin, et al., Acta Mat. 53, 4029 (2005)). More information and a correction can be found in the FAQ. Update 17 Jan. 2014: Prof. Mishin noted that "Our ADP Ta potential has a known error: the elastic constants predicted by the potential as a factor of two different from those reported in the paper. This was the result of a bug in the fitting code that was used during the potential development. All other properties are exactly as reported in the paper. The mixed Cu-Ta interactions are also fine. However, because of this error in the elastic constants, the potential cannot be recommended for studying mechanical properties of pure Ta." Update: The 2015--Purja-Pun-G-P--Cu-Ta ADP potential has supplanted this potential.

ADP tabulated functions
Notes: These files were provided by Yuri Mishin (George Mason University) and posted on 22 Jan. 2010.
File(s): superseded

Citation: X.W. Zhou, R.A. Johnson, and H.N.G. Wadley (2004), "Misfit-energy-increasing dislocations in vapor-deposited CoFe/NiFe multilayers", Physical Review B, 69(14), 144113. DOI: 10.1103/physrevb.69.144113.
Abstract: Recent molecular dynamics simulations of the growth of [Ni0.8Fe0.2/Au] multilayers have revealed the formation of misfit-strain-reducing dislocation structures very similar to those observed experimentally. Here we report similar simulations showing the formation of edge dislocations near the interfaces of vapor-deposited (111) [NiFe/CoFe/Cu] multilayers. Unlike misfit dislocations that accommodate lattice mismatch, the dislocation structures observed here increase the mismatch strain energy. Stop-action observations of the dynamically evolving atomic structures indicate that during deposition on the (111) surface of a fcc lattice, adatoms may occupy either fcc sites or hcp sites. This results in the random formation of fcc and hcp domains, with dislocations at the domain boundaries. These dislocations enable atoms to undergo a shift from fcc to hcp sites, or vice versa. These shifts lead to missing atoms, and therefore a later deposited layer can have missing planes compared to a previously deposited layer. This dislocation formation mechanism can create tensile stress in fcc films. The probability that such dislocations are formed was found to quickly diminish under energetic deposition conditions.

Notes: These are the original files sent by X.W. Zhou (Sandia National Laboratory) and posted with his permission. C.A. Becker (NIST) modified create.f to include the reference in the generated potential files and the EAM.input file for this composition. These files can be used to generate alloy potentials for Cu, Ag, Au, Ni, Pd, Pt, Al, Pb, Fe, Mo, Ta, W, Mg, Co, Ti, and Zr by editing EAM.input. However, as addressed in the reference, these potentials were not designed for use with metal compounds.
File(s): superseded

LAMMPS pair_style eam/alloy (2004--Zhou-X-W--Ta-Cu--LAMMPS--ipr1)
Notes: This file was generated by C.A. Becker (NIST) from create.f and posted with X.W. Zhou's (Sandia National Laboratory) permission. The tabulations in this file are identical to the tabulations in the "CuTa.eam.alloy" file in the August 22, 2018 LAMMPS distribution.
File(s): superseded

Notes: The file Zhou04_create_v2.f is an updated version of create.f modified by L.M. Hale (NIST) following advice from X.W. Zhou (Sandia National Laboratory). This version removes spurious fluctuations in the tabulated functions of the original potential files caused by single/double precision floating point number conflicts.
LAMMPS pair_style eam/alloy (2004--Zhou-X-W--Ta-Cu--LAMMPS--ipr2)
Notes: This file was generated by L.M. Hale from Zhou04_create_v2.f on 13 April 2018 and posted with X.W. Zhou's (Sandia National Laboratory) permission. This version corrects an issue with spurious fluctuations in the tabulated functions.
Date Created: October 5, 2010 | Last updated: October 05, 2018