Pair_style hybrid

LAMMPS LAMMPS Beginners
1

Hi everyone.
I hope you are doing well.
I am a beginner in LAMMPS and just recently started working with LAMMPS. In this way, I watched and worked on tutorials from Simon’s work.
However, recently, I wanted to do a simulation (using LAMMPS 14 May 2016) and did not set it up by myself. I just downloaded the original files from the following link on github:

I just wanted to run it and see the results they showed.
However, I am getting the following error:
ERROR: Illegal pair_style command (…/pair_lj_cut_coul_long.cpp:600)
I searched a lot and noticed this is a common error and many have faced it before me; however, the cases are different in terms of the pair_style command they used.
As you can see in the original file, the pair_ style is as follows:
pair_style hybrid lj/cut/tip4p/long 1 2 1 1 0.1250 8.5 8.5 lj/cut/coul/long 8.5 8.5 airebo 3.0

I read the manual about the hybrid. I did not notice anything that could be the cause.
I would be appreciative if you could give me a hint on this.
Thank you so much.

2

You should not start with an 8 year old version of LAMMPS. This version has known bugs, is missing many features and nobody will be willing to help you.

3

Have you checked, if your LAMMPS executable contains the MANYBODY package and thus the airebo pair style. With old versions of LAMMPS the keywords “airebo 3.0” would be passed to the previous pair style, if airebo is not included and thus cause the error message you see.

When using a recent version of LAMMPS you would get a better error message.

5

thank you for the hint.
I ran it with newer version (LAMMPS 2 Aug 2023) and got the following error:
ERROR on proc 0: Potential file does not match AIREBO/REBO style variant: # AIREBO : # need to cite the appropriate papers here 1.0 eV = 23.06 kcal/mol

(src/MANYBODY/pair_airebo.cpp:3384)

Last command: pair_coeff * * airebo CH.airebo_real NULL NULL NULL NULL C C

So, I am thinking about the pair_coefficient, and I have to check it if it is correct or not.

6

The problem is with the CH.airebo_real file. The error message is quite clear about this. This seems to be modified relative to what is bundled with LAMMPS and thus likely not compatible with the currently code.

7

Thank you so much.
Do you have any suggestions on where I need to start to fix the problem?

8

You can use the potential file bundled with LAMMPS.

9

Thanks for the suggestion.
I just used either of these potentials available in the installation directory, CH.airebo and CH.airebo-m, and got this error:
ERROR on proc 0: airebo potential file CH.airebo requires metal units but real units are in use (src/potential_file_reader.cpp:285)

Last command: pair_coeff * * airebo CH.airebo NULL NULL NULL NULL C C

So, I simply changed units real to units metal and got the following error:
WARNING: Using a manybody potential with bonds/angles/dihedrals and special_bond exclusions (src/pair.cpp:242)
WARNING: Communication cutoff adjusted to 12.2 (src/comm.cpp:732)
Per MPI rank memory allocation (min/avg/max) = 294.9 | 294.9 | 294.9 Mbytes
Step Temp Press Volume TotEng
243 405.97654 -1.0569831e+295 554029.94 -24328.535
ERROR: Out of range atoms - cannot compute PPPM (src/KSPACE/pppm_tip4p.cpp:108)
Last command: run 250000
So this means I have to focus on the way PPPM works.

10

You cannot just change the units keyword. You have to adjust all pair_coeff terms according to those different units.

Look at this crazy pressure here. That suggests that your geometry has some close contacts.
The out-of-range error is just a consequence of that.

This topic has been discussed many times, so we don’t need to repeat it here.

No.

11

Thanks.
That was a silly mistake I made. Makes sense as pair coefficients were written in real units and basically the epsilon needed to be changed (kcal/mol to eV).
Now, it runs.