The way that Langevin thermostatting operates is explained on the fix +langevin doc page. If you wish to simply viscously +damp the rotational motion without thermostatting, you can set +Tstart and Tstop to 0.0, which means only the viscous drag term in +the Langevin thermostat will be applied. See the discussion on the +fix viscous doc page for details.
IMPORTANT NOTE: When the langevin keyword is used with fix rigid versus fix rigid/small, different dynamics will result for parallel diff --git a/doc/fix_rigid.txt b/doc/fix_rigid.txt index 948b8e14ee..ef3e98025b 100644 --- a/doc/fix_rigid.txt +++ b/doc/fix_rigid.txt @@ -377,8 +377,14 @@ 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). The random # {seed} must be a positive -integer. The way the Langevin thermostatting operates is explained on -the "fix langevin"_fix_langevin.html doc page. +integer. + +The way that Langevin thermostatting operates is explained on the "fix +langevin"_fix_langevin.html doc page. If you wish to simply viscously +damp the rotational motion without thermostatting, you can set +{Tstart} and {Tstop} to 0.0, which means only the viscous drag term in +the Langevin thermostat will be applied. See the discussion on the +"fix viscous"_doc/fix_viscous.html doc page for details. IMPORTANT NOTE: When the {langevin} keyword is used with fix rigid versus fix rigid/small, different dynamics will result for parallel diff --git a/doc/fix_viscous.html b/doc/fix_viscous.html index 2140a7e8cc..9d890a071a 100644 --- a/doc/fix_viscous.html +++ b/doc/fix_viscous.html @@ -76,11 +76,14 @@ needed, gamma can be adjusted for atoms of different sizes force term to thermostat the system at a chosen temperature. The fix langevin command does this. It has the same viscous damping term as fix viscous and adds a random force to each -atom. Hence if using fix langevin you do not typically need to use -fix viscous. Also note that the gamma of fix viscous is related to -the damping parameter of fix langevin, except that -the units of gamma are force/velocity and the units of damp are time, -so that it can more easily be used as a thermostat. +atom. The random force term is proportional to the sqrt of the chosen +thermostatting temperature. Thus if you use fix langevin with a +target T = 0, its random force term is zero, and you are essentially +performing the same operation as fix viscous. Also note that the +gamma of fix viscous is related to the damping parameter of fix +langevin, however the former is specified in units +of force/velocity and the latter in units of time, so that it can more +easily be used as a thermostat.