how to generate eam/fs format potential file?

Dear LAMMPS users,

I am having the Finnis_Sinclair potential parameters and equations describing the pair interaction as well as electron density. Please find the pdf file attached with this mail (equation 6 to 9 gives the FS potential energy formulae and table 7 potential parameters).

I wanted to generate eam/fs style potential file using the above details.

I have small query related to eam/fs format!!,

basically the potential files of types eam/fs pair style lists (copying few lines from LAMMPS mannual),

  • lines 1,2,3 = comments (ignored)
  • line 4: Nelements Element1 Element2 … ElementN
  • line 5: Nrho, drho, Nr, dr, cutoff

followed by (lines for single element file)

  • line 1 = atomic number, mass, lattice constant, lattice type

  • embedding function F(rho) (Nrho values)

  • density function rho® for element 1 at element 1 (Nr values)

  • Nr values of pair potential phi®
    The question is F(rho) is a function of rho, which depends on the number of atoms with in the cutoff radius specified. the number of atoms in the cutoff may vary during the simulation and thus the electron density at any atom which in turn varies the Embedding energy. SO, embedding energy being dynamically varying how its values are tabulated. Is it assumed that the electron density varies between max and min value for which it is tabulated?

if yes, how the max and min value of electron density is found for a given element?

If I am wrong please correct me.

thanking you in advance
&

with regards

Kiran

JApplPhys_93_3328.pdf (403 KB)

Dear LAMMPS users,

I am having the Finnis_Sinclair potential parameters and equations
describing the pair interaction as well as electron density. Please find the
pdf file attached with this mail (equation 6 to 9 gives the FS potential
energy formulae and table 7 potential parameters).
I wanted to generate eam/fs style potential file using the above details.

I have small query related to eam/fs format!!,

basically the potential files of types eam/fs pair style lists (copying few
lines from LAMMPS mannual),

lines 1,2,3 = comments (ignored)
line 4: Nelements Element1 Element2 ... ElementN
line 5: Nrho, drho, Nr, dr, cutoff

followed by (lines for single element file)

line 1 = atomic number, mass, lattice constant, lattice type
embedding function F(rho) (Nrho values)
density function rho(r) for element 1 at element 1 (Nr values)
Nr values of pair potential phi(r)

The question is F(rho) is a function of rho, which depends on the number of
atoms with in the cutoff radius specified. the number of atoms in the cutoff
may vary during the simulation and thus the electron density at any atom
which in turn varies the Embedding energy. SO, embedding energy being
dynamically varying how its values are tabulated. Is it assumed that the
electron density varies between max and min value for which it is tabulated?

yes. between zero and a maximum value to be more specific.

if yes, how the max and min value of electron density is found for a given
element?

there are some C/Fortran programs in the "tools" directory of the
LAMMPS source tree that construct EAM potential files as they are used
by LAMMPS from published parameter information. have a look. might be
helpful.

axel.

Is it assumed that the

electron density varies between max and min value for which it is tabulated?

yes. between zero and a maximum value to be more specific.

if yes, how the max and min value of electron density is found for a given
element?

The EAM files have a drho and Nrho value you specify in the header.
So 0.0 is the min and the max = Nrho * drho. It’s up to you to choose
a physically meaningful max value. I believe that if the code ever
encounters a density value > max, that it just uses the last value
in the table as the F(rho) value.

Steve

Dear Dr. Steve and Axel,

I think I need to find the equilibrium electron density rhoe.I think taking a value slightly above rhoe value, I have to define the embedding energy F(1.15*rho) and check the properties.

and

Thank you for the help.

with regards

Kiran