lammps/doc/temper.txt

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:link(lc,Section_commands.html#comm)

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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_nh.html, "temp/berendsen"_fix_nh.html,
"langevin"_fix_langevin.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.

As a tempering run proceeds, multiple log files and screen output
files are created, one per replica.  By default these files are named
log.lammps.M and screen.M where M is the replica number from 0 to N-1,
with N = # of replicas.  See the "section on command-line
switches"_Section_start.html#2_6 for info on how to change these
names.

The main screen and log file (log.lammps) will list information about
which temperature is assigned to each replica at each thermodynamic
output timestep.  E.g. for a simulation with 16 replicas:

Running on 16 partitions of processors
Step T0 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15
0    0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
500  1 0 3 2 5 4 6 7 8 9 10 11 12 13 14 15
1000 2 0 4 1 5 3 6 7 8 9 10 11 12 14 13 15
1500 2 1 4 0 5 3 6 7 9 8 10 11 12 14 13 15
2000 2 1 3 0 6 4 5 7 10 8 9 11 12 14 13 15
2500 2 1 3 0 6 4 5 7 11 8 9 10 12 14 13 15
... :pre

The column headings T0 to TN-1 mean which temperature is currently
assigned to the replica 0 to N-1.  Thus the columns represent replicas
and the value in each column is its temperature (also numbered 0 to
N-1).  For example, a 0 in the 4th column (column T3, step 2500) means
that the 4th replica is assigned temperature 0, i.e. the lowest
temperature.  You can verify this time sequence of temperature
assignments for the Nth replica by comparing the Nth column of screen
output to the thermodynamic data in the corresponding log.lammps.N or
screen.N files as time proceeds.

The last argument {index} in the temper command 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 the following for a simulation with 5 replicas:

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