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@ -10,69 +10,62 @@ fix grem command :h3
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[Syntax:]
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fix ID group-ID grem lambda eta H0 thermostat-ID
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fix ID group-ID grem lambda eta H0 thermostat-ID :pre
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ID, group-ID are documented in "fix"_fix.html command
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grem = style name of this fix command
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lambda = intercept parameter of linear effective temperature function
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eta = slope parameter of linear effective temperature function
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H0 = shift parameter of linear effective temperature function
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thermostat-ID = ID of thermostat used in simulation
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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grem = style name of this fix command :l
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lambda = intercept parameter of linear effective temperature function :l
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eta = slope parameter of linear effective temperature function :l
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H0 = shift parameter of linear effective temperature function :l
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thermostat-ID = ID of Nose-Hoover thermostat or barostat used in simulation :l,ule
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[Examples:]
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fix fxgREM all grem 400 -0.01 -30000 fxnpt
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thermo_modify press fxgREM_press
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thermo_modify press fxgREM_press :pre
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fix fxgREM all grem 502 -0.15 -80000 fxnvt
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fix fxgREM all grem 502 -0.15 -80000 fxnvt :pre
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[Description:]
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This fix implements the molecular dynamics version
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of the generalized replica
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exchange method (gREM) originally developed by "(Kim)"_#Kim,
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which uses non-Boltzmann ensembles to sample over first
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order phase transitions.
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The is done by defining replicas with an enthalpy dependent
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This fix implements the molecular dynamics version of the generalized
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replica exchange method (gREM) originally developed by "(Kim)"_#Kim,
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which uses non-Boltzmann ensembles to sample over first order phase
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transitions. The is done by defining replicas with an enthalpy dependent
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effective temperature
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:c,image(Eqs/fix_grem.jpg)
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with {eta} negative and steep enough to only intersect
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the characteristic microcanonical temperature (Ts) of the
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system once, ensuring a unimodal enthalpy distribution in
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that replica. {Lambda} is the intercept and effects the
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generalized ensemble similar to how temperature effects
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a Boltzmann ensemble. {H0} is a reference enthalpy, and
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is typically set as the lowest desired sampled enthalpy.
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Further explanation can be found in our recent papers
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"(Malolepsza)"_#Malolepsza.
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with {eta} negative and steep enough to only intersect the characteristic
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microcanonical temperature (Ts) of the system once, ensuring a unimodal
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enthalpy distribution in that replica. {Lambda} is the intercept and
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effects the generalized ensemble similar to how temperature effects a
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Boltzmann ensemble. {H0} is a reference enthalpy, and is typically set
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as the lowest desired sampled enthalpy. Further explanation can be
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found in our recent papers "(Malolepsza)"_#Malolepsza.
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This fix requires a thermostat, with ID passed to fix_grem
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by {thermostat-ID}. Two distinct temperatures exist in this
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generalized ensemble, the effective temperature defined above,
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and a kinetic temperature that controls the velocity
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distribution of particles as usual. Either constant volume
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or constant pressure algorithms can be used.
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This fix requires a Nose-Hoover thermostat reference passed to the grem
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by {thermostat-ID}. Two distinct temperatures exist in this generalized
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ensemble, the effective temperature defined above, and a kinetic
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temperature that controls the velocity distribution of particles as
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usual. Either constant volume or constant pressure algorithms can be
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used.
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The fix enforces a generalized ensemble in a single replica
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only. Typically, different replicas only differ by {lambda}
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for simplicity, but this is not necessary. Multi-replica
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runs need to be run outside of LAMMPS. An example of this
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can be found in examples/USER/misc/grem
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The fix enforces a generalized ensemble in a single replica only.
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Typically, different replicas only differ by {lambda} for simplicity,
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but this is not necessary. Multi-replica runs need to be run outside
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of LAMMPS. An example of this can be found in examples/USER/misc/grem
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In general, defining the generalized ensembles is unique for
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every system. When starting a many-replica simulation without
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any knowledge of the underlying microcanonical temperature,
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there are several tricks we have utilized to optimize the process.
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Choosing a less-steep {eta} yields broader distributions,
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requiring fewer replicas to map the microcanonical temperature.
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While this likely struggles from the same sampling problems
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gREM was built to avoid, it provides quick insight to Ts.
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Initially using an evenly-spaced {lambda} distribution identifies
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In general, defining the generalized ensembles is unique for every
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system. When starting a many-replica simulation without any knowledge of
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the underlying microcanonical temperature, there are several tricks we
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have utilized to optimize the process. Choosing a less-steep {eta}
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yields broader distributions, requiring fewer replicas to map the
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microcanonical temperature. While this likely struggles from the same
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sampling problems gREM was built to avoid, it provides quick insight to
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Ts. Initially using an evenly-spaced {lambda} distribution identifies
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regions where small changes in enthalpy lead to large temperature
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changes. Replicas are easily added where needed.
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changes. Replicas are easily added where needed.
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:line
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@ -93,8 +86,7 @@ LAMMPS"_Section_start.html#start_3 section for more info.
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[Related commands:]
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"fix_nh"_fix_nh.html
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"thermo_modify"_thermo_modify.html
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"fix nvt"_fix_nh.html, "fix npt"_fix_nh.html, "thermo_modify"_thermo_modify.html
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[Default:] none
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Axel Kohlmeyer