create a precipitate

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1

Hi,

I use this syntax to create voids in the structure , for ex:
region void0 sphere 20 20 25 0.5
delete_atoms region void0

However, is there any way to create precipitates in the structure. I am looking to add a group of interstitial atoms in the structure or a region of interstitial atoms ? I don’t know if this is possible or not, I am new to LAMMPS

Thanks
Mo

2

You can use create_atoms or read_data multiple times

to add new atoms to a set of existing atoms. However, it is up

to you to insure that the final collection of atoms makes geometric

sense, e.g. does not overlap too strongly. If that’s not

possible/easy to do, you are likely better off using some pre-processing

geometry builder to create a data file for LAMMPS to read. See

the pre/post web page on the LAMMPS web site for examples.

Steve

3

Hi,

I use the pair_style zbl with a pair_coeff as follow:

pair_style hybrid eam/cd zbl 1.0 2.05

pair_coeff * * …/potentials/FeCr.cdeam Fe Cr
pair_coeff 2 2 zbl 24.0 24.0
pair_coeff 1 2 zbl 26.0 24.0

I use the EAM potential with zbl.
My concern regarding the pair_coeff command. As I understand that atomic number for two atom types should be associated with the pair coefficient command. I use the atomic number of 26 and 24 for both Fe and Cr, respectively. Is this correct to use? is there any restrictions to this command while using the atomic number?

Thanks
Mo

4

There is delete_atoms and create_atoms. The

latter can insert atoms on a lattice within

a geometric region. It can also use a “molecule”

file that defines a set of atoms that it will

insert wherever you like. It’s up to you

to insure the final structure is reasonable,

e.g. no overlaps. LAMMPS has various ways

to relax overlaps (e.g. minimize).

Steve

5

This question is covered in the documentation, under Mixing. You script contains a variety of syntax and conceptual errors. you should instead do something like this (I did not test this, so it may still be incorrect):

hybrid/overlay adds all potential contributions together

pair_style hybrid/overlay eam/cd zbl 1.0 2.05

with hybrid or hybrid/overlay, each argument list must begin with the pair_style name

pair_coeff * * eam/cd …/potentials/FeCr.cdeam Fe Cr

zbl coefficients are required for all pure pairs

pair_coeff 1 1 zbl 26.0 26.0
pair_coeff 2 2 zbl 24.0 24.0

zbl coefficients for mixed pairs are required with hybrid/overlay

pair_coeff 1 2 zbl 26.0 24.0

Aidan

6

Thanks for the help all.

Aidan

I changed the script and it works fine using hybrid/overlay for mixed pairs.

I have one last question, I am doing zbl to harden/ stiffen the potential, however, the Fe-Fe part is already stiffened in the potential. Do I need to apply the zbl to Fe-Fe part again? or I can just do zbl for Fe-Cr and Cr-Cr parts since Fe-Fe is already stiffened?

in addition, you mentioned that the zbl coefficients are required for all pure pairs.

Thanks in advance

7

I can not tell you how to build a correct model. You will have to figure that out yourself. LAMMPS does require that all pure pairs be specified. If you wish the ZBL interaction to be zero for Fe-Fe, the code is not set up to support that. You can trick it by making the Z values small, but not too small, so that for the smallest separations encountered in the simulation, the function phi (see doc page) evaluates to a sufficiently small value (say 1e-6).