"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 temp/berendsen command :h3 [Syntax:] fix ID group-ID temp/berendsen Tstart Tstop Tdamp :pre ID, group-ID are documented in "fix"_fix.html command :ulb,l temp/berendsen = style name of this fix command :l Tstart,Tstop = desired temperature at start/end of run :l Tstart can be a variable (see below) :pre Tdamp = temperature damping parameter (time units) :l,ule [Examples:] fix 1 all temp/berendsen 300.0 300.0 100.0 :pre [Description:] Reset the temperature of a group of atoms by using a Berendsen thermostat "(Berendsen)"_#Berendsen, which rescales their velocities every timestep. The thermostat is applied to only the translational degrees of freedom for the particles, which is an important consideration for finite-size particles which have rotational degrees of freedom are being thermostatted with this fix. The translational degrees of freedom can also have a bias velocity removed from them before thermostatting takes place; see the description below. The desired temperature at each timestep is a ramped value during the run from {Tstart} to {Tstop}. The {Tdamp} parameter is specified in time units and determines how rapidly the temperature is relaxed. For example, a value of 100.0 means to relax the temperature in a timespan of (roughly) 100 time units (tau or fmsec or psec - see the "units"_units.html command). {Tstart} can be specified as an equal-style "variable"_variable.html. In this case, the {Tstop} setting is ignored. If the value is a variable, it should be specified as v_name, where name is the variable name. In this case, the variable will be evaluated each timestep, and its value used to determine the target temperature. Equal-style variables can specify formulas with various mathematical functions, and include "thermo_style"_thermo_style.html command keywords for the simulation box parameters and timestep and elapsed time. Thus it is easy to specify a time-dependent temperature. NOTE: Unlike the "fix nvt"_fix_nh.html command which performs Nose/Hoover thermostatting AND time integration, this fix does NOT perform time integration. It only modifies velocities to effect thermostatting. Thus you must use a separate time integration fix, like "fix nve"_fix_nve.html to actually update the positions of atoms using the modified velocities. Likewise, this fix should not normally be used on atoms that also have their temperature controlled by another fix - e.g. by "fix nvt"_fix_nh.html or "fix langevin"_fix_langevin.html commands. See "this howto section"_Section_howto.html#howto_16 of the manual for a discussion of different ways to compute temperature and perform thermostatting. This fix computes a temperature each timestep. To do this, the fix creates its own compute of style "temp", as if this command had been issued: compute fix-ID_temp group-ID temp :pre See the "compute temp"_compute_temp.html command for details. Note that the ID of the new compute is the fix-ID + underscore + "temp", and the group for the new compute is the same as the fix group. Note that this is NOT the compute used by thermodynamic output (see the "thermo_style"_thermo_style.html command) with ID = {thermo_temp}. This means you can change the attributes of this fix's temperature (e.g. its degrees-of-freedom) via the "compute_modify"_compute_modify.html command or print this temperature during thermodynamic output via the "thermo_style custom"_thermo_style.html command using the appropriate compute-ID. It also means that changing attributes of {thermo_temp} will have no effect on this fix. Like other fixes that perform thermostatting, this fix can be used with "compute commands"_compute.html that calculate a temperature after removing a "bias" from the atom velocities. E.g. removing the center-of-mass velocity from a group of atoms or only calculating temperature on the x-component of velocity or only calculating temperature for atoms in a geometric region. This is not done by default, but only if the "fix_modify"_fix_modify.html command is used to assign a temperature compute to this fix that includes such a bias term. See the doc pages for individual "compute commands"_compute.html to determine which ones include a bias. In this case, the thermostat works in the following manner: the current temperature is calculated taking the bias into account, bias is removed from each atom, thermostatting is performed on the remaining thermal degrees of freedom, and the bias is added back in. :line [Restart, fix_modify, output, run start/stop, minimize info:] No information about this fix is written to "binary restart files"_restart.html. The "fix_modify"_fix_modify.html {temp} option is supported by this fix. You can use it to assign a temperature "compute"_compute.html you have defined to this fix which will be used in its thermostatting procedure, as described above. For consistency, the group used by this fix and by the compute should be the same. The "fix_modify"_fix_modify.html {energy} option is supported by this fix to add the energy change implied by a velocity rescaling to the system's potential energy as part of "thermodynamic output"_thermo_style.html. This fix computes a global scalar which can be accessed by various "output commands"_Section_howto.html#howto_15. The scalar is the cummulative energy change due to this fix. The scalar value calculated by this fix is "extensive". This fix can ramp its target temperature over multiple runs, using the {start} and {stop} keywords of the "run"_run.html command. See the "run"_run.html command for details of how to do this. This fix is not invoked during "energy minimization"_minimize.html. [Restrictions:] This fix can be used with dynamic groups as defined by the "group"_group.html command. Likewise it can be used with groups to which atoms are added or deleted over time, e.g. a deposition simulation. However, the conservation properties of the thermostat and barostat are defined for systems with a static set of atoms. You may observe odd behavior if the atoms in a group vary dramatically over time or the atom count becomes very small. [Related commands:] "fix nve"_fix_nve.html, "fix nvt"_fix_nh.html, "fix temp/rescale"_fix_temp_rescale.html, "fix langevin"_fix_langevin.html, "fix_modify"_fix_modify.html, "compute temp"_compute_temp.html, "fix press/berendsen"_fix_press_berendsen.html [Default:] none :line :link(Berendsen) [(Berendsen)] Berendsen, Postma, van Gunsteren, DiNola, Haak, J Chem Phys, 81, 3684 (1984).