In LAMMPS, does MC or MD happen first?

LAMMPS LAMMPS Beginners
1

Dear all
I might be encountering a technical issue. In LAMMPS, does MC or MD happen first?

Here is a part of my code:

fix 1 all nvt temp 500 500 10
fix 2 all gcmc 10 10 10 3 62513 500 -3.6 0.1
thermo 1

This means that MD operations will be performed throughout the process, and only at specific steps will MC operations take place. From the stepwise output in the log file, I can see that GCMC operations occur at step 1 and step 11. What I’m curious about is, in the steps with GCMC, like step 11, does LAMMPS first perform the GCMC operation and then the MD, or does it perform MD first and then GCMC?
With regards!

2

Neither. If you look at the general flow of control of a timestep show here: 4.7. How a timestep works — LAMMPS documentation
Then fix gcmc is invoked at the “pre_exchange” stage.

That means after the initial integrate (i.e. after the first half step velocity update and the full step position update), but before the neighbor list update and force force computation and the final integrate step with the second half step velocity update).

3

Thank you for your reply. I think I understand it a bit better now. I’ll take some time to study it more carefully.