[lammps-users] A question about pair_coeff command


If there are 3 types of atoms and the following input script is used

pair_coeff * * 0.0 0.0
pair_coeff 1 1 1.0 1.0
pair_coeff 2 2 2.0 2.0

Then, the pair coeff between type 1 and type 2 is zero? Or, the coeff between type 1 and type 2 is calculated by some mix rule?




My understanding of the docs at:


is that the pair coeffs between type 1 and type 2
would be zero for the example you've given.


Dear list:

     My question is about `dump' command. I wrote a script to run the MD
simulation. It will start simulation, stop it to check, and restart it if
equilibrium is not reached. What I hope is, however many times it is
restarted, all simulation results should be written to a single dump file.
But apparently lammps will overwrite dump file every run ( if the same dump
file is reused next time). Is it possible to tell lammps not to overwrite but
append dump information to an existing file?
     By the way, I think probably 'time_stamp' is a better word than
'reset_timestep' for the command of setting simulation time info, for the
latter can be confused with 'timestep', is it?



Hi Jiwu. Short answer on your dump question is: no,
LAMMPS doesn't have that option. Once execution of
LAMMPS has ceased, you can't restart LAMMPS and append
to the end of existing dump files. I'd recommend just
concatenating your dump files from the command line
with something like: "cat dump.* > alldumps".

On the reset_timestep command, I do see what you mean
and agree that some other command word might have been
less confusing than "reset_timestep", but I'm not sure
it is worth changing the code and the docs at this
stage ...

Thanks for your input; I hope this helps!


If you hadn’t used the pair_coeff * * 0 0 command, but just the other
2, then LAMMPS would do default mixing as described in the doc for the pair_modify