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. These parameter providers have different names in Asap version 2 and 3.

Potential parameters in Asap version 3.

EMTStandardParameters
The default EMT parameters, as published in [3].
EMTRasmussenParameters
An alternative set of parameters for Cu, Ag and Au, reoptimized to experimental data including the stacking fault energies by Torben Rasmussen.
EMThcpParameters
EMT parameters for pure HCP metals. Currenlty, only Ruthenium is supported [6]. Do not use this potential, it is really bad!
EMTMetalGlassParameters
EMT parameters for MgCu and CuZr metallic glasses [4, 5].

Examples:

A calculation with default EMT parameters:

atoms.set_calculator(EMT())

A calculation with Torben Rasmussen's parameters:

atoms.set_calculator(EMT(EMTRasmussenParameters()))

A calculation for CuZr metallic glass:

atoms.set_calculator(EMT(EMTMetalGlassParameters()))

Potential parameters in Asap version 2.

The following parameter providers are available.

EMTDefaultParameterProvider
The default EMT parameters, as published in [3].
EMTRasmussenParameterProvider
An alternative set of parameters for Cu and Ag, reoptimized to experimental data including the stacking fault energies by Torben Rasmussen.
EMTAtomicUnitParameterProvider
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.
EMTVariableParameterProvider
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.
EMThcpParameterProvider
Similar to EMTVariableParameterProvider but for HCP metals. Can currently be used for Ruthenium.
GetPotential()

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.

Parameters for metallic glasses have been optimized by Nick Bailey and Anca Paduraru.

Examples (Asap version 2)

A calculation with default EMT parameters:

atoms.SetCalculator(EMT())

A calculation with Torben Rasmussen's parameters:

atoms.SetCalculator(EMT(EMTRasmussenParameterProvider()))

A calculation for CuZr metallic glass:

from Asap.Utilities.GetPotential import GetPotential
atoms.SetCalculator(GetPotential("EMT-CuZr-glass.dat"))

References

[1]

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.

[2]

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.

[3]

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.

[4]

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.

[5]

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.

[6]

J. Gavnholt and J. Schiøtz: The structure and reactivity of Ruthenium nanoparticles, Phys. Rev. B 77, 035404 (2008).

The parameters for Ru are given in endnote 21.

Asap: EMT (last edited 2012-02-16 10:03:16 by JakobSchiøtz)