# How can I reduce time-step with dt/reset command?

Hi friends,
How can I reduce the timestep to something like 0.1 fs with dt/reset command in LAMMPS?
I wrote a sample but I think it’s wrong.
My unit is “metal”

# fix 3 all dt/reset 1 NULL 0.001 0.1 emax 30.0 units box

Thanks.

Why?

Because I can’t understand very well the algorithm of reducing timestep.
How does it work?
I read the documentation completely, but it had not written anything about reducing. I want to know how can I reduce the timestep? and its algorithm if possible.

Thanks.

It works as it is described in the documentation. If you do not understand the documentation you need to explain in detail what you do not understand and why. Also you need to explain what you want to achieve and for what purpose.

I need to understand what params can control the timestep and reduce that?
And I want to simulate a radiation damage on CuZr with high energies.
and better describe the atomic trajectories at high velocities.

This does not answer my question

When I radiate a high energy ion (like 15 KeV) , atoms are moving too far in a single time-step. I want to reduce that to describe the damage or other changes.
when I radiate it, the energy goes from my table. (unreasonable.)
range of energies in table -----> 10 eV - 10 MeV

I don’t understand what you are talking about. What has this to do with how fix dt/reset works? Its algorithm is straightforward and there are no tables involved.

Also, changing the time step will not change the energy of atoms, it will only change how many steps it will take to to pass a certain amount of simulation time.

1 Like

Thanks, you are right.
That’s exactly what I meant.
and I need to reduce the timestep to achieve this.

Is my fix command correct?

Thanks again.

You do not understand. I cannot help people that do not pay attention to what I tell them.

I know what you are saying, but I don’t know how to explain it.

I see nothing wrong with this example. If you just want to reduce timestep to 0.1 fs, use the command “timestep 0.0001”, you will have a fixed timestep = 0.1 fs during simulation.

fix ID group-ID dt/reset N Tmin Tmax Xmax command will give you variable timestep, it resets your timestep every N steps so that no atom moves further than the specified Xmax distance or no atom’s kinetic energy changes by more than the specified Emax