forked from lijiext/lammps
91 lines
3.0 KiB
Plaintext
91 lines
3.0 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
|
|
|
|
:link(lws,http://lammps.sandia.gov)
|
|
:link(ld,Manual.html)
|
|
:link(lc,Section_commands.html#comm)
|
|
|
|
:line
|
|
|
|
fix dt/reset command :h3
|
|
|
|
[Syntax:]
|
|
|
|
fix ID group-ID dt/reset N Tmin Tmax Xmax keyword values ... :pre
|
|
|
|
ID, group-ID are documented in "fix"_fix.html command
|
|
dt/reset = style name of this fix command
|
|
N = recompute dt every N timesteps
|
|
Tmin = minimum dt allowed (can be INF) (time units)
|
|
Tmax = maximum dt allowed (can be INF) (time units)
|
|
Xmax = maximum distance for an atom to move in one timestep (distance units)
|
|
zero or more keyword/value pairs may be appended
|
|
keyword = {units} :ul
|
|
{units} value = {lattice} or {box}
|
|
lattice = Xmax is defined in lattice units
|
|
box = Xmax is defined in simulation box units :pre
|
|
|
|
[Examples:]
|
|
|
|
fix 5 all dt/reset 10 1.0e-5 0.01 0.1
|
|
fix 5 all dt/reset 10 0.01 2.0 0.2 units box :pre
|
|
|
|
[Description:]
|
|
|
|
Reset the timestep size every N steps during a run, based on current
|
|
atom velocities and forces. This can be useful when starting from a
|
|
configuration with overlapping atoms, where forces will be large. Or
|
|
it can be useful when running an impact simulation where one or more
|
|
high-energy atoms collide with a solid, causing a damage cascade.
|
|
|
|
This fix overrides the timestep size setting made by the
|
|
"timestep"_timestep.html command. The new timestep size {dt} is
|
|
computed in the following way.
|
|
|
|
compute Vmax of any atom in group
|
|
compute Amax of any atom in group
|
|
dt1 = Xmax/Vmax
|
|
dt2 = sqrt(2 Xmax/Amax)
|
|
new dt = MIN(dt1,dt2)
|
|
if dt < Tmin, dt = Tmin
|
|
if dt > Tmax, dt = Tmax :ul
|
|
|
|
Vmax is the maximum velocity; Amax is the maximum acceleration =
|
|
force/mass. Note that Tmin or Tmax can be specified as INF, in which
|
|
case one or both of the last 2 checks will not be performed.
|
|
|
|
When the "run style"_run_style.html is {respa}, this fix resets the
|
|
outer loop (largest) timestep, which is the same timestep that the
|
|
"timestep"_timestep.html command sets.
|
|
|
|
[Restart, fix_modify, output, run start/stop, minimize info:]
|
|
|
|
No information about this fix is written to "binary restart
|
|
files"_restart.html. None of the "fix_modify"_fix_modify.html options
|
|
are relevant to this fix.
|
|
|
|
The current timestep size is stored as a scalar quantity by this fix.
|
|
The cumulative simulation time (in time units) is stored as the first
|
|
element of a vector. Both these quantities can be accessed by various
|
|
"output commands"_Section_howto.html#4_15. The scalar and vector
|
|
values calculated by this fix are "intensive", meaning they are
|
|
independent of the number of atoms in the simulation.
|
|
|
|
No parameter of this fix can be used with the {start/stop} keywords of
|
|
the "run"_run.html command. This fix is not invoked during "energy
|
|
minimization"_minimize.html.
|
|
|
|
[Restrictions:]
|
|
|
|
The cumulative time is zeroed when the fix is created and
|
|
continuously accrues thereafter. Using the
|
|
"reset_timestep"_reset_timestep.html command while this fix is defined
|
|
will mess up the time accumulation.
|
|
|
|
[Related commands:]
|
|
|
|
"timestep"_timestep.html
|
|
|
|
[Default:]
|
|
|
|
The option defaults is units = lattice.
|