Running a simulation backward in time

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1

Hi all,
I want simulate a system(Brownian particles crossing a potential barrier) which runs backward in time. Is it possible use a negative value in time step or do i have to use a negative initial velocity?

Thank you,
Diljith T

2

Hi all,
I want simulate a system(Brownian particles crossing a potential barrier) which runs backward in time. Is it possible use a negative value in time step or do i have to use a negative initial velocity?

to reverse a simulation you have to flip the sign of the velocity components. something like this (untested):

variable vx atom -vx
variable vy atom -vy
variable vz atom -vz

velocity set v_vx v_vy v_vz

please note that exact reversibility is only possible for NVE ensemble simulations (i.e. without thermostat or random forces) and fixed point math (LAMMPS uses floating point math).

axel.

3

Which is the way the LAMMPS logo on the webpage was animated.
Run N timesteps, flip the sign of the velocities, run N more steps.

Steve

4

Thanks.

5

In case you don’t already know, the links above and below the LAMMPS logo on the project home page (input script, physical analog and explanation) all seem to come up empty.

-David

6

I just fixed the link above the animation, pointing to the input script that generated the animation.
The 2 links below must have gone extinct at YouTube and Yale. I would insert
a joke here about YouTube outliving Yale, but apparently it was a close call.

Steve