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Citation: A. Nichol, and G.J. Ackland (2016), "Property trends in simple metals: An empirical potential approach", Physical Review B, 93(18), 184101. DOI: 10.1103/physrevb.93.184101.
Abstract: We demonstrate that the melting points and other thermodynamic quantities of the alkali metals can be calculated based on static crystalline properties. To do this we derive analytic interatomic potentials for the alkali metals fitted precisely to cohesive and vacancy energies, elastic moduli, the lattice parameter, and crystal stability. These potentials are then used to calculate melting points by simulating the equilibration of solid and liquid samples in thermal contact at ambient pressure. With the exception of lithium, remarkably good agreement is found with experimental values. The instability of the bcc structure in Li and Na at low temperatures is also reproduced and, unusually, is not due to a soft T1N phonon mode. No forces or finite-temperature properties are included in the fit, so this demonstrates a surprisingly high level of intrinsic transferability in the simple potentials. Currently, there are few potentials available for the alkali metals, so in addition to demonstrating trends in behavior, we expect that the potentials will be of broad general use.

Notes: G.J. Ackland noted that lattice parameters, elastic constants and cohesive energies were used in the fitting process, so the values produced by this conversion should match known values. He noted that bcc crystal structure should be stable and produce a melting temperature of 370 K. Publication information was updated on 12 Oct. 2017. Prior publication listing for this potential was Han, S., Zepeda-Ruiz, L. A., Ackland, G. J., Car, R., and Srolovitz, D. J. (2003). Interatomic potential for vanadium suitable for radiation damage simulations. Journal of Applied Physics, 93(6), 3328. DOI: 10.1063/1.1555275

Moldy FS
Notes: The parameters in Na.moldy were obtained from http://homepages.ed.ac.uk/graeme/moldy/moldy.html and posted with the permission of G.J. Ackland.
File(s):
LAMMPS pair_style eam/fs (2016--Nichol-A--Na--LAMMPS--ipr1)
Notes: This conversion was performed by G.J. Ackland and submitted on 8 Dec. 2015.
File(s): superseded


LAMMPS pair_style eam/fs (2016--Nichol-A--Na--LAMMPS--ipr2)
Notes: A new conversion to LAMMPS performed by G.J. Ackland was submitted on 10 Oct. 2017. The previous setfl version above had a spurious oscillation period in the tabulated r*phi function that influenced measurements, most notably static elastic constant evaluations.
File(s):
Citation: S.R. Wilson, K.G.S.H. Gunawardana, and M.I. Mendelev (2015), "Solid-liquid interface free energies of pure bcc metals and B2 phases", The Journal of Chemical Physics, 142(13), 134705. DOI: 10.1063/1.4916741.
Abstract: The solid-liquid interface (SLI) free energy was determined from molecular dynamics (MD) simulation for several body centered cubic (bcc) metals and B2 metallic compounds (space group: Pm-3m; prototype: CsCl). In order to include a bcc metal with a low melting temperature in our study, a semi-empirical potential was developed for Na. Two additional synthetic "Na" potentials were also developed to explore the effect of liquid structure and latent heat on the SLI free energy. The obtained MD data were compared with the empirical Turnbull, Laird, and Ewing relations. All three relations are found to predict the general trend observed in the MD data for bcc metals obtained within the present study. However, only the Laird and Ewing relations are able to predict the trend obtained within the sequence of "Na" potentials. The Laird relation provides the best prediction for our MD data and other MD data for bcc metals taken from the literature. Overall, the Laird relation also agrees well with our B2 data but requires a proportionality constant that is substantially different from the bcc case. It also fails to explain a considerable difference between the SLI free energies of some B2 phases which have nearly the same melting temperature. In contrast, this difference is satisfactorily described by the Ewing relation. Moreover, the Ewing relation obtained from the bcc dataset also provides a reasonable description of the B2 data.

Notes: Mikhail Mendelev (Ames Laboratory) noted that his potential was designed to simulate solid-liquid interface properties in sodium. Updated 27 Apr 2015 to include publication information.

LAMMPS pair_style eam/fs (2015--Wilson-S-R--Na--LAMMPS--ipr1)
Notes: This file was provided by Mikhail Mendelev (Ames Laboratory) and posted with his permission on 14 Nov. 2014. He noted that his potential was designed to simulate solid-liquid interface properties in sodium.
Updated 27 Apr 2015 to include publication information.
File(s):
Date Created: October 5, 2010 | Last updated: October 02, 2018