From b58c43a5ec151daf2b694206aa6b97fc5ff02cba Mon Sep 17 00:00:00 2001
From: sjplimp <sjplimp@f3b2605a-c512-4ea7-a41b-209d697bcdaa>
Date: Tue, 30 Jun 2009 22:51:36 +0000
Subject: [PATCH] git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@2933
 f3b2605a-c512-4ea7-a41b-209d697bcdaa

---
 doc/fix_viscous.html | 9 +++++++--
 doc/fix_viscous.txt  | 9 +++++++--
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/doc/fix_viscous.html b/doc/fix_viscous.html
index bb29f6ec52..e52fa4c056 100644
--- a/doc/fix_viscous.html
+++ b/doc/fix_viscous.html
@@ -57,6 +57,11 @@ optional keyword <I>scale</I> is used, gamma can scaled up or down by the
 specified factor for atoms of that type.  It can be used multiple
 times to adjust gamma for several atom types.
 </P>
+<P>IMPORTANT NOTE: You should specify gamma in force/velocity units.
+This is not the same as mass/time units, at least for some of the
+LAMMPS <A HREF = "units.html">units</A> options like "real" or "metal" that are not
+self-consistent.
+</P>
 <P>In a Brownian dynamics context, gamma = kT / D, where k = Boltzmann's
 constant, T = temperature, and D = particle diffusion coefficient.  D
 can be written as kT / (3 pi eta d), where eta = dynamic viscosity of
@@ -76,8 +81,8 @@ viscous damping term as fix viscous and adds a random force to each
 atom.  Hence if using fix <I>langevin</I> you do not typically need to use
 fix <I>viscous</I>.  Also note that the gamma of fix viscous is related to
 the damping parameter of <A HREF = "fix_langevin.html">fix langevin</A>, except that
-the units of gamma are force/velocity (or mass/time) and the units of
-damp are time, so that it can more easily be used as a thermostat.
+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.
 </P>
 <P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
 </P>
diff --git a/doc/fix_viscous.txt b/doc/fix_viscous.txt
index f2cf5aa467..31f6f2a591 100644
--- a/doc/fix_viscous.txt
+++ b/doc/fix_viscous.txt
@@ -47,6 +47,11 @@ optional keyword {scale} is used, gamma can scaled up or down by the
 specified factor for atoms of that type.  It can be used multiple
 times to adjust gamma for several atom types.
 
+IMPORTANT NOTE: You should specify gamma in force/velocity units.
+This is not the same as mass/time units, at least for some of the
+LAMMPS "units"_units.html options like "real" or "metal" that are not
+self-consistent.
+
 In a Brownian dynamics context, gamma = kT / D, where k = Boltzmann's
 constant, T = temperature, and D = particle diffusion coefficient.  D
 can be written as kT / (3 pi eta d), where eta = dynamic viscosity of
@@ -66,8 +71,8 @@ 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"_fix_langevin.html, except that
-the units of gamma are force/velocity (or mass/time) and the units of
-damp are time, so that it can more easily be used as a thermostat.
+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.
 
 [Restart, fix_modify, output, run start/stop, minimize info:]