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.

EMT Potential parameters

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()))

Equations

The equations implemented in the EMT potential are documented here: emt.pdf.

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.