"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

temper command :h3

[Syntax:]

temper N M temp fix-ID seed1 seed2 index :pre

N = total # of timesteps to run
M = attempt a tempering swap every this many steps
temp = initial temperature for this ensemble
fix-ID = ID of the fix that will control temperature during the run
seed1 = random # seed used to decide on adjacent temperature to partner with
seed2 = random # seed for Boltzmann factor in Metropolis swap 
index = which temperature (0 to N-1) I am simulating (optional) :ul

[Examples:]

temper 100000 100 $t tempfix 0 58728
temper 40000 100 $t tempfix 0 32285 $w :pre

[Description:]

Run a parallel tempering (replica exchange) simulation of multiple
ensembles of a system on multiple partitions of processors.  The
processor partitions are defined using the -partition command-line
switch (see "this section"_Section_start.html#2_6).  Each ensemble's
temperature is typically controlled at a different value by a fix with
ID {fix-ID} that controls temperature.  Possible fix styles are
"nvt"_fix_nvt.html, "npt"_fix_npt.html, and
"temp/rescale"_fix_temp_rescale.html.  The desired temperature is
specified by {temp}, which is typically a variable previously set in
the input script, so that each partition is assigned a different
temperature.  See the "variable"_variable.html command for more
details.  For example,

variable t world 300.0 310.0 320.0 330.0 :pre

As the tempering simulation runs for {N} timesteps, a swap between
adjacent ensembles will be attempted every {M} timesteps.  If {seed1}
is 0, then the swap attempts will alternate between odd and even
pairings.  If {seed1} is non-zero then it is used as a seed in a
random number generator to randomly choose an odd or even pairing each
time.  Each attempted swap of temperatures is either accepted or
rejected based on a Boltzmann-weighted Metropolis criterion which uses
{seed2} in the random number generator.

The last argument {index} is optional and is used when restarting a
tempering run from a set of restart files (one for each replica) which
had previously swapped to new temperatures.  The {index} value (from 0
to N-1, where N is the # of replicas) identifies which temperature the
replica was simulating on the timestep the restart files were written.
Obviously, this argument must be a variable so that each partition has
the correct value.  Set the variable to the {N} values listed in the
log file for the previous run for the replica temperatures at that
timestep.  For example if the log file listed

500000 2 4 0 1 3 :pre

then a setting of

variable w proc 2 4 0 1 3 :pre

would be used to restart the run with a tempering command like the
example above with $w as the last argument.

[Restrictions:] none

[Related commands:]

"variable"_variable.html

[Default:] none