Setforce command extension

Hello all,

I am new to LIGGGHTS and I am practicing some simulations with test - crack examples. There I found this command set force - “fix 2 mobile setforce 0.0 2 0.0”

Now if I need to apply force at “an angle” on a point/atom is it possible by this command or do I need to change the inbuilt libraries and recompile? Also can anyone please let me know if there is any step by step tutorial to change and recompile liggghts to customize?

Regarding the version I use - I have downloaded and updated with latest git resource but still when I type liggghts command in terminal I get this - “LIGGGHTS 1.5 based on lammps-10Mar10” am I missing something here?

Thanks a lot for replies and apologies for naive questions if any :slight_smile:



The setforce args are forces in the x,y,z dirs. If you specify
both a x and y component then it will be at an “angle”.


Hello Steve, thank you so much for the reply.

I tried that one but I guess I am doing it wrong? When I applied some force in X direction instead of ZERO i.e. now in force in both x,y directions the crack is instead one direction, the crack also in both directions. I want it to be angular or crack in uniform expansion in X, Y directions. Please find the attached for the output.

Can you please also tell me 1. Why there are uneven atom visualization at the top of the structre

  1. By crack means we are forcing and moving atoms away?

Thanks a lot for replies!


don’t know - I’m telling you how LAMMPS works, not what
might be wrong with your model. You can verify the added forces
from setforce are what I said by dumping them.