Eam files

Dear Sir,

I want to know can I couple two different eam files with hybrid pair_style. Suppose I have a ternary system of Fe-Cr-Ni, Am I allowed to use Fe-Cr.cdeam and Fe-Ni.eam potential files available within LAMMPS, to simulate for the properties for my ternary system. I think if I do so, interactions between Cr and Ni is not being provided.

Is their any way to do so.?

Agraj

You can use pair hybrid with any combination of pair styles.
However, what doesn't make sense about your model is that
Fe is part of both. For manybody potentials like EAM, you
need to construct the model so that a set of atom types (e.g. the
Fe type) is part of just one sub-style. It doesn't make sense
(in a manybody) sense for an Fe atom to get a contribution
to its density functional from 2 different kinds of atoms, computed
by two different potentials.

What you could do instead is build one EAM model using
all 3 elements, and one EAM file that represents all
the interactions. And then you don't need pair hybrid.

Steve

Thanks for the reply sir.

1). you wrote about constructing a model to have one sub-style. I can use FeCr.cdeam potential for Fe and Cr element. Now either I can add Ni eam file at the end of FeCr.cdeam to get one eam file or can I use Ni eam file, hybrid with cdeam file. Is it the way in which eam is constructed.??

2). Agrain for building one eam, can I add Fe, Ni, Cr eam files in one to generate one eam file representing all interactions. If it can be done so, then what about first four-five lines parameters.

I have also gone through the eam doc page, in which the four-five lines says well what to include. I think if I go that way then I will have to go for curve fitting and potential development to get the interaction potentials.

I request you to tell me, what does constructing and building of eam file mean, and how it can be done.

Agraj

Thanks for the reply sir.

1). you wrote about constructing a model to have one sub-style. I can use
FeCr.cdeam potential for Fe and Cr element. Now either I can add Ni eam file
at the end of FeCr.cdeam to get one eam file or can I use Ni eam file,
hybrid with cdeam file. Is it the way in which eam is constructed.??

not really.

2). Agrain for building one eam, can I add Fe, Ni, Cr eam files in one to
generate one eam file representing all interactions. If it can be done so,
then what about first four-five lines parameters.

have a look at the tools/eam_database directory in the lammps distribution
and the corresponding paper. this could be a starting point in learning how to
build eam/alloy files.

I have also gone through the eam doc page, in which the four-five lines says
well what to include. I think if I go that way then I will have to go for
curve fitting and potential development to get the interaction potentials.

yes.

I request you to tell me, what does constructing and building of eam file
mean, and how it can be done.

read the papers that document it.

LAMMPS provides the tools to _use_ eam potentials, but
_constructing_ potentials is an entirely different business.

first rule for that is really understanding the potential function
and "philosophy" behind it and that requires to read the
corresponding literature.

cheers,
    axel.

Dear Sir,

Thanks for the reply. I have gone as per your instructions. And at last I am able to make set file from fortran code available in tools/eam_database. I could make TaCu.set as Ta and Cu is available by default. And these set files can be used with eam.alloy pair_style.

Now I would like to know, it is so that the equations provided in the subroutines for calculating pair potential, embedding energy, electron density, will be different for different binary and ternary system.

If its like that then do I have to look for the functions in literature, for calculating above required parameters.

Or Am I allowed to use the available functions in subroutines, and only change the atomtype in EAM.input file for different system…

Agraj

Dear Sir,

Thanks for the reply. I have gone as per your instructions. And at last I am
able to make set file from fortran code available in tools/eam_database. I
could make TaCu.set as Ta and Cu is available by default. And these set
files can be used with eam.alloy pair_style.

Now I would like to know, it is so that the equations provided in the
subroutines for calculating pair potential, embedding energy, electron
density, will be different for different binary and ternary system.

why don't you just read the paper that goes with the tool?
or do you need somebody to read it to you???

axel.

As I said before:

What you could do instead is build one EAM model using
all 3 elements, and one EAM file that represents all
the interactions.

That file can have any of the formats that LAMMPS supports,
e.g. eam/alloy, eam/fs. If's up to you to create the
file with the correct format for the elements you want.

Steve

Dear Sir,

Few days back I asked about potential generation from tools available in LAMMPS.

Now I would like to know, for example, suppose I take four different elements Nickel, Zirconium, Aluminium, Lead, available from two different eam files toghether. Will the script below give me interactions between all the elements. Can I use hybrid pair style for eam potentials in this way.?

I have run the simulation, its running well, but I fear if it’s wrong. Also, how can I check whether all the elements are interacting or not.?

Thanks,

Agraj



create_box 2 box
create_atoms 1 box

pair_style hybrid/overlay eam/fs eam/alloy
pair_coeff * * eam/fs Ni-Zr.eam.fs Ni Zr
pair_coeff * * eam/alloy Al-Pb.eam.alloy Al Pb

variable e equal pe

No, that's not correct. If it runs at all, your simulation must
have 2 atom types, since that's all you list on each pair_coeff command.
So how do you have 2 types to represent 4 elements?

More generally, you cannot mix many-body potentials like this. You
need to create one EAM file in a single format (e.g. eam/alloy) that
contains all the cross interactions you want. And you need to
create this yourself by merging fields from different files you have.
Unless one of the tools provided will build an alloy system like
you want. And then run it with a single pair_style eam/alloy
command.

Steve