Hybrid of MEAM and LJ potential

LAMMPS LAMMPS Development
1

Greetings!
I am trying to use hybrid of MEAM and LJ potential for studying Hydrogen diffusivity in Nb-Ta-Ti-V-Zr alloy. I am employing MEAM potential to model the metal-metal interactions and LJ potential for metal-hydrogen atom interaction. However, pair coefficient command for MEAM potential is showing error " Cannot open library file". Here’s the few lines of the LAMMPS (Version- April 2021) code:

units metal
echo both
atom_style atomic
dimension 3
boundary p p p

read_data NbTaTiVZr_Hydrogen_box

mass 1 50.942 #V
mass 2 92.9060 #Nb
mass 3 180.9480 #Ta
mass 4 47.8800 #Ti
mass 5 91.2200 #Zr
mass 6 1.008 #H

timestep 0.002

#--------------------------FORCE FIELDS--------------------------------------

pair_style hybrid meam lj/cut 10.0

pair_coeff 1 5 meam VNbTaTiZr.library.meam V Nb Ta Ti Zr VNbTaTiZr.parameter.meam V Nb Ta Ti Zr NULL

Lennard-Jones potential for Hydrogen

pair_coeff 6 6 lj/cut 0.0104 3.4 # Example parameters for H-H interaction

Cross interactions between EAM/alloy atoms and LJ atoms

pair_coeff 1 6 lj/cut 0.0150 3.2 # Ni-H interaction
pair_coeff 2 6 lj/cut 0.0150 3.2 # Fe-H interaction
pair_coeff 3 6 lj/cut 0.0150 3.2 # Cr-H interaction
pair_coeff 4 6 lj/cut 0.0150 3.2 # Co-H interaction
pair_coeff 5 6 lj/cut 0.0150 3.2 # Cu-H interaction
neigh_modify every 1 delay 0 check yes

#-----------------------ENERGY MINIMISATION-------------------------------------

min_style cg
minimize 1.0e-12 1.0e-12 500000 500000

I would highly appreciate any suggestion.

2

Well, is the library file where your command says it is?

This is almost 4 years old. You should use a recent release of LAMMPS. Many bugs have been fixed and error messages improved.

3

I used the latest LAMMPS version and checked the code just using meam potential. It worked. However when I am using hybrid pair style to I am getting error. I believe I am going wrong in the command. I need 5 atom types metallic interaction (V,Nb,Ti,Zr,Ta) with meam potential and the LJ potential for Hydrogen-metal interactions separately. Do i need to assign each metal-metal interactions separately?I went through the manual and tried. Its not working.

command : pair_coeff 1 2 meam VNbTaTiZr.library.meam V Nb Ta Ti Zr VNbTaTiZr.parameter.meam V Nb Ta Ti Zr

The errors I am getting “Incorrect arguments for pair coefficient” and " Cannot open library file"
I will appreciate any suggestion.

4

This is a useless description, since what is the “latest version” changes over time and where you look and how you install LAMMPS. The only unambiguous description is the version info from lmp -h. Also see: 1.2. What does a LAMMPS version mean — LAMMPS documentation

This command cannot be correct, since MEAM requires pair_coeff * * like most many-body potentials.

This error message clearly means that LAMMPS cannot find the file where you specified it would be. That usually means that either your input as a typo or the file is not in the current working directory where you run your input or - in case your LAMMPS_POTENTIALS environment variable is set, it is not pointing to the correct folder.

That often means, there are not enough arguments. From your description it sounds that you have six atom types in your system, but your pair_coeff command only specifies 5 elements to map. There must be as many elements as there are atom types. If there is an atom type you don’t want to map (like your hydrogen atom type), you must use NULL. This is all explained in great detail in the LAMMPS documentation for the pair_coeff, the pair_style meam, and the pair_style hybrid commands.

5

This is a wild guess, but are you by chance running on a Windows machine?
If yes, than the filename for the library file may not be what the Windows file explorer shows you, since it will by default chop off any file extensions.