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< title > fix langevin/eff command — LAMMPS documentation< / title >
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< li > fix langevin/eff command< / li >
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< span id = "index-0" > < / span > < h1 > fix langevin/eff command< a class = "headerlink" href = "#fix-langevin-eff-command" title = "Permalink to this headline" > ¶< / a > < / h1 >
< div class = "section" id = "syntax" >
< h2 > Syntax< a class = "headerlink" href = "#syntax" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > fix ID group-ID langevin/eff Tstart Tstop damp seed keyword values ...
< / pre > < / div >
< / div >
< ul class = "simple" >
< li > ID, group-ID are documented in < a class = "reference internal" href = "fix.html" > < em > fix< / em > < / a > command< / li >
< li > langevin/eff = style name of this fix command< / li >
< li > Tstart,Tstop = desired temperature at start/end of run (temperature units)< / li >
< li > damp = damping parameter (time units)< / li >
< li > seed = random number seed to use for white noise (positive integer)< / li >
< li > zero or more keyword/value pairs may be appended< / li >
< / ul >
< pre class = "literal-block" >
keyword = < em > scale< / em > or < em > tally< / em > or < em > zero< / em >
< em > scale< / em > values = type ratio
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type = atom type (1-N)
ratio = factor by which to scale the damping coefficient
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< em > tally< / em > values = < em > no< / em > or < em > yes< / em >
< em > no< / em > = do not tally the energy added/subtracted to atoms
< em > yes< / em > = do tally the energy added/subtracted to atoms
< / pre >
< pre class = "literal-block" >
< em > zero< / em > value = < em > no< / em > or < em > yes< / em >
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< em > no< / em > = do not set total random force to zero
< em > yes< / em > = set total random force to zero
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< / pre >
< / div >
< div class = "section" id = "examples" >
< h2 > Examples< a class = "headerlink" href = "#examples" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > fix 3 boundary langevin/eff 1.0 1.0 10.0 699483
fix 1 all langevin/eff 1.0 1.1 10.0 48279 scale 3 1.5
< / pre > < / div >
< / div >
< / div >
< div class = "section" id = "description" >
< h2 > Description< a class = "headerlink" href = "#description" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > Apply a Langevin thermostat as described in < a class = "reference internal" href = "#schneider" > < span > (Schneider)< / span > < / a >
to a group of nuclei and electrons in the < a class = "reference internal" href = "pair_eff.html" > < em > electron force field< / em > < / a > model. Used with < a class = "reference internal" href = "fix_nve_eff.html" > < em > fix nve/eff< / em > < / a > ,
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this command performs Brownian dynamics (BD), since the total force on
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each atom will have the form:< / p >
< div class = "highlight-python" > < div class = "highlight" > < pre > F = Fc + Ff + Fr
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Ff = - (m / damp) v
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Fr is proportional to sqrt(Kb T m / (dt damp))
< / pre > < / div >
< / div >
< p > Fc is the conservative force computed via the usual inter-particle
interactions (< a class = "reference internal" href = "pair_style.html" > < em > pair_style< / em > < / a > ).< / p >
< p > The Ff and Fr terms are added by this fix on a per-particle basis.< / p >
< p > The operation of this fix is exactly like that described by the < a class = "reference internal" href = "fix_langevin.html" > < em > fix langevin< / em > < / a > command, except that the thermostatting
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is also applied to the radial electron velocity for electron
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particles.< / p >
< / div >
< div class = "section" id = "restart-fix-modify-output-run-start-stop-minimize-info" >
< h2 > Restart, fix_modify, output, run start/stop, minimize info< a class = "headerlink" href = "#restart-fix-modify-output-run-start-stop-minimize-info" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > No information about this fix is written to < a class = "reference internal" href = "restart.html" > < em > binary restart files< / em > < / a > . Because the state of the random number generator
is not saved in restart files, this means you cannot do “ exact”
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restarts with this fix, where the simulation continues on the same as
if no restart had taken place. However, in a statistical sense, a
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restarted simulation should produce the same behavior.< / p >
< p > The < a class = "reference internal" href = "fix_modify.html" > < em > fix_modify< / em > < / a > < em > temp< / em > option is supported by this
fix. You can use it to assign a temperature < a class = "reference internal" href = "compute.html" > < em > compute< / em > < / a >
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you have defined to this fix which will be used in its thermostatting
procedure, as described above. For consistency, the group used by
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this fix and by the compute should be the same.< / p >
< p > The < a class = "reference internal" href = "fix_modify.html" > < em > fix_modify< / em > < / a > < em > energy< / em > option is supported by this
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fix to add the energy change induced by Langevin thermostatting to the
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system’ s potential energy as part of < a class = "reference internal" href = "thermo_style.html" > < em > thermodynamic output< / em > < / a > . Note that use of this option requires
setting the < em > tally< / em > keyword to < em > yes< / em > .< / p >
< p > This fix computes a global scalar which can be accessed by various
< a class = "reference internal" href = "Section_howto.html#howto-15" > < span > output commands< / span > < / a > . The scalar is the
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cummulative energy change due to this fix. The scalar value
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calculated by this fix is “ extensive” . Note that calculation of this
quantity requires setting the < em > tally< / em > keyword to < em > yes< / em > .< / p >
< p > This fix can ramp its target temperature over multiple runs, using the
< em > start< / em > and < em > stop< / em > keywords of the < a class = "reference internal" href = "run.html" > < em > run< / em > < / a > command. See the
< a class = "reference internal" href = "run.html" > < em > run< / em > < / a > command for details of how to do this.< / p >
< p > This fix is not invoked during < a class = "reference internal" href = "minimize.html" > < em > energy minimization< / em > < / a > .< / p >
< / div >
< div class = "section" id = "restrictions" >
< h2 > Restrictions< a class = "headerlink" href = "#restrictions" title = "Permalink to this headline" > ¶< / a > < / h2 >
< blockquote >
< div > none< / div > < / blockquote >
< p > This fix is part of the USER-EFF package. It is only enabled if
LAMMPS was built with that package. See the < a class = "reference internal" href = "Section_start.html#start-3" > < span > Making LAMMPS< / span > < / a > section for more info.< / p >
< / div >
< div class = "section" id = "related-commands" >
< h2 > Related commands< a class = "headerlink" href = "#related-commands" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > < a class = "reference internal" href = "fix_langevin.html" > < em > fix langevin< / em > < / a > < / p >
< / div >
< div class = "section" id = "default" >
< h2 > Default< a class = "headerlink" href = "#default" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > The option defaults are scale = 1.0 for all types and tally = no.< / p >
< hr class = "docutils" / >
< p id = "dunweg" > < strong > (Dunweg)< / strong > Dunweg and Paul, Int J of Modern Physics C, 2, 817-27 (1991).< / p >
< p id = "schneider" > < strong > (Schneider)< / strong > Schneider and Stoll, Phys Rev B, 17, 1302 (1978).< / p >
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© Copyright 2013 Sandia Corporation.
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