eam/fs self potential files


I am looking to simulate crystalline tungsten using LAMMPS with finis-sinclair type potentials. These are not readily available from the nist repository and therefore I am currently in the process of producing my own tabulated setfl potential files using a python script. To test my understanding of tabulated eam/fs potentials I tested it on the tabulated finnis-sinclair Molybdenum potential [1]. However, the interatomic potential I produced only matched with the tabulated potential upon introducing factors of 2 in the expressions for phi [2], not present in the original 1987 Ackland and Thetford paper. Upon introducing these factors, I can reproduce [1] up to the number of printed decimal places. These factors only seem to be applied to the original pair-potential due to Finnis and Sinclair and do not apply to the Ackland and Thetford corrections. I have been reading around the subject but I am unable to find a satisfactory explanation as to why the factors of 2 are there.

Furthermore, I have run tests using these potential files to find the lattice parameter, and they are close but not quite right (3.157 for Mo, 3.11 for W).

Can someone give me an explanation please?

Best wishes,

Jonas Verschueren

[1] http://www.ctcms.nist.gov/potentials/Mo.html, third entry in the list.
[2] def phi®:
if r<b0 and r< c:
return (2*(r-c)2(c0+c1r+c2r*2)+B*(b0-r)*3np.exp(-alphar))
elif r<c:
return 2*(r-c)2(c0+c1r+c2r
return 0

You can read about how LAMMPS does eam/fs in the doc page

(which gives the format of the potential file) and in the source

code: pair_eam_fs.cpp.