create eam/alloy from eam

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1

Dear lammps users,

There are two eam-potential file in setfl format :Al.eam.alloy, Ce.eam.alloy.

I am trying to create Al-Ce potential file in setfl format by using this mixing rule:
(PHYSICAL REVIEW B VOLUME 39, NUMBER 17 “Alloy models with the embedded-atom method” R. A. Johnson):

f1 = fa® / fb®

f2 = fb® / fa®

Z2R1 = f1 * Z2Rb®

Z2R2 = f2 * Z2Ra®

Z2Rab® = 0.5*( Z2R1 + Z2R2)

I get the wrong result,
Please help me how can I mix them?

I will be of great pleasure to hear from you.
Regards

Tohid Naseri
2

The pair_style eam doc page describes the format of the alloy
file. Note that it says:

Unlike the effective charge array Z(r) in funcfl files, the tabulated
values for each phi function are listed in setfl files directly as
r*phi (in units of eV-Angstroms), since they are for atom pairs.

And that above that it gives some details about units:

For two interacting atoms i,j this is used by LAMMPS to compute the
pair potential term in the EAM energy expression as r*phi, in units of
eV-Angstroms, via the formula

r*phi = 27.2 * 0.529 * Zi * Zj

where 1 Hartree = 27.2 eV and 1 Bohr = 0.529 Angstroms.

Steve

3

Dear Steve,

Thank you for your reply,
I read lammps documentation about eam and eam/alloy pair_styles and setfl and funcfl file format.
Also I studied Pair_eam.cpp and Pair_eam_alloy.cpp, carefully.
I realized differences of single element potential file in funcfl format and setfl format that are:
1- file header
2-order of arrays
3-Z2R values versus effective charge

I can convert single element funcfl format to single element setfl format
by using this equation: Z2R = 27.20.529zri*zri. After this conversion,
I run two simulation by same properties with this difference that the first
simulation used funcfl format with eam pair_style, and the second simulation
used setfl format with eam/alloy pair_style. Results were identical with each other.

By using the above equation, funcfl format conversion to setfl format is simple,
but reverse conversion (setfl to funcfl) is impossible because of negative values in
setfl format.

I am searching for a eam mixing rule that can mix Al.eam.alloy and Ce.eam.alloy
for Al-Ce interaction, these two single element potential files are in setfl format.
Lammps documentation say eam pair_style can mix two funcfl file automatically:
Z2R = 27.20.529zri*zrj
But according to the above descriptions (setfl conversion to funcfl is impossible)
I should look the other ways for mixing these two files.

I worked with lammps tools directory (eam_generate and eam_database),
eam_database tools creates binary setfl potential file that read eam parameters
from EAM_code file but Cerium eam parameters are not included. So this tool can’t help me.

According to the eam_database tool and this paper (PHYSICAL REVIEW B VOLUME 39, NUMBER 17
“Alloy models with the embedded-atom method” R. A. Johnson),

I used below mixing rule:

f1 = fa® / fb®

f2 = fb® / fa®

Z2R1 = f1 * Z2Rb®

Z2R2 = f2 * Z2Ra®

Z2Rab® = 0.5*( Z2R1 + Z2R2)

I did above instructions by AWK and made one potential file in setfl format that include Al-Ce
pair potential.
I start Al-Ce simulation at 100 K,by Beta_Ce3Al structure
(Qiao-Shi Zenga et al. Substitutional alloy of Ce and Al. PNAS, February 24, 2009 vol. 106 no. 8 2515-2518)
Unfortunately during simulation after first time step, results showed extremely increasing
in volume, and the alloy structure destroyed at 100K temperature that caused stopping me.

I did same instructions for Cu.eam.alloy and Zr.eam.alloy too, (B2 structure) but similar conclusion
was reached !

How can I mix these files?

Best Regards,
Tohid Naseri
Master student of Nanotechnology engineering

4

By using the above equation, funcfl format conversion to setfl format is simple,
but reverse conversion (setfl to funcfl) is impossible because of negative values in
setfl format.

am searching for a eam mixing rule that can mix Al.eam.alloy and Ce.eam.alloy
for Al-Ce interaction

If you want a new AlCe setfl alloy file, then I don’t see why you need to mess with
funcfl files at all. An alloy file for 2 elements lists the pure Al and pure Ce and mixed
AlCe interactions explcitly, all in setfl format. So you can tabullate the cross
interaction directly.

Steve