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Effective Medium Theory (EMT)
The EMT potential is the main Calculator in Asap, and the raison d'être of Asap. It is a many-body potential, giving a good description of the late transition metals crystalling in the FCC crystal structure. The elements described by the main set of EMT parameters are Al, Ni, Cu, Pd, Ag, Pt, and Au, the Al potential is however not suitable for materials science application, as the stacking fault energy is wrong.
In addition to the default EMT parameters, it is possible to use a ParameterProvider to provide an alternative set of EMT parameters. In this way, it is possible to use EMT potentials for Ru as well as for Mg-Cu and Cu-Zr metallic glasses.
The following parameter providers are available.
- The default EMT parameters, as published in .
- An alternative set of parameters for Cu and Ag, reoptimized to experimental data including the stacking fault energies by Torben Rasmussen.
- The default EMT parameters for simulations where distances are interpreted as in bohr instead of Å, and time units are changed similarly. Do not use unless you know what you are doing. In fact, using this is probably a sign of not knowing what you are doing. It will soon be removed.
- Allows the parameters to be set individually from Python. This provider is used for optimization, but is also used for the metallic glass EMT parameters together with the GetPotential function.
- Similar to EMTVariableParameterProvider but for HCP metals. Can currently be used for Ruthenium.
- A function reading EMT parameters from a file, and returning an EMT potential with a EMTVariableParameterProvider attached. The files containing metallic glass parameters will soon be published here.
EMT parameters for metallic glasses
Parameters for metallic glasses have been optimized by Nick Bailey and Anca Paduraru.
A calculation with default EMT parameters:
A calculation with Torben Rasmussen's parameters:
A calculation for CuZr metallic glass:
from Asap.Utilities.GetPotential import GetPotential atoms.SetCalculator(GetPotential("EMT-CuZr-glass.dat"))
K. W. Jacobsen, J. K. Nørskov and M. J. Puska: "Interatomic interactions in the effective-medium theory", Phys. Rev. B 35, 7423 (1987).
This is the original paper presenting EMT. The detailed formulation has changed somewhat since.
K. W. Jacobsen: "Bonding in metallic systems: an effective medium approach", Comm. Cond. Matter Phys. B14, 129 (1988)
A paedagogical exposition of the ideas behind EMT.
K. W. Jacobsen, P. Stoltze and J. K. Nørskov: "A semi-empirical effective medium theory for metals and alloys", Surf. Sci. 366, 394 (1996).
The modern formulation of EMT. The Asap implementation follows this formulation, and the default EMT parameters are the ones published here.
N. P. Bailey, J. Schiøtz and K. W. Jacobsen: "Simulation of Cu-Mg Metallic Glass: Thermodynamics and Structure", Phys. Rev. B 69, 144205 (2004).
The parameters for the MgCu metallic glass was published here.
A. Paduraru, A. Kenoufi, N. P. Bailey and J. Schiøtz: "An Interatomic Potential for Studying CuZr Bulk Metallic Glasses", Adv. Eng. Mater. 9, 505 (2007).
The parameters for the CuZr metallic glass.