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Added zerosum option 

git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@5858 f3b2605a-c512-4ea7-a41b-209d697bcdaa
This commit is contained in:
athomps 2011-03-28 00:13:42 +00:00
parent fae9ea3b79
commit 56f53d83cc
2 changed files with 36 additions and 6 deletions
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21
doc/fix_langevin.html
View File

@ -33,7 +33,10 @@
ratio = factor by which to scale the damping coefficient
<I>tally</I> values = <I>no</I> or <I>yes</I>
<I>no</I> = do not tally the energy added/subtracted to atoms
<I>yes</I> = do tally the energy added/subtracted to atoms
<I>yes</I> = do tally the energy added/subtracted to atoms
<I>zerosum</I> values = <I>no</I> or <I>yes</I>
<I>no</I> = do not set total random force to zero
<I>yes</I> = set total random force to zero
</PRE>
</UL>
@ -146,13 +149,24 @@ particle mass in Ff, unlike fix <I>viscous</I>. Thus the mass and size of
different atom types should be accounted for in the choice of ratio
values.
</P>
<P>The keyword <I>tally</I> enables the calculation of the cummulative energy
<P>The keyword <I>tally</I> enables the calculation of the cumulative energy
added/subtracted to the atoms as they are thermostatted. Effectively
it is the energy exchanged between the infinite thermal reservoir and
the particles. As described below, this energy can then be printed
out or added to the potential energy of the system to monitor energy
conservation.
</P>
<P>The keyword <I>zerosum</I> can be used to eliminate drift due to the
thermostat. Because the random forces on
different atoms are independent, they
do not sum exactly to zero. As a result, this fix applies a
small random force to the entire system, and the center-of-mass
of the system undergoes a slow random walk. If the keyword <I>zerosum</I>
is set to <I>yes</I>, the total random force is set exactly to zero
by subtracting off an equal part of it from each atom in the group.
As a result, the center-of-mass of a system with zero initial momentum
will not drift over time.
</P>
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
</P>
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
@ -196,7 +210,8 @@ dpd/tstat</A>
</P>
<P><B>Default:</B>
</P>
<P>The option defaults are scale = 1.0 for all types and tally = no.
<P>The option defaults are scale = 1.0 for all types, tally = no,
zerosum = yes.
</P>
<HR>

21
doc/fix_langevin.txt
View File

@ -24,7 +24,10 @@ keyword = {scale} or {tally}
ratio = factor by which to scale the damping coefficient
{tally} values = {no} or {yes}
{no} = do not tally the energy added/subtracted to atoms
{yes} = do tally the energy added/subtracted to atoms :pre
{yes} = do tally the energy added/subtracted to atoms
{zerosum} values = {no} or {yes}
{no} = do not set total random force to zero
{yes} = set total random force to zero :pre
:ule
[Examples:]
@ -136,13 +139,24 @@ particle mass in Ff, unlike fix {viscous}. Thus the mass and size of
different atom types should be accounted for in the choice of ratio
values.
The keyword {tally} enables the calculation of the cummulative energy
The keyword {tally} enables the calculation of the cumulative energy
added/subtracted to the atoms as they are thermostatted. Effectively
it is the energy exchanged between the infinite thermal reservoir and
the particles. As described below, this energy can then be printed
out or added to the potential energy of the system to monitor energy
conservation.
The keyword {zerosum} can be used to eliminate drift due to the
thermostat. Because the random forces on
different atoms are independent, they
do not sum exactly to zero. As a result, this fix applies a
small random force to the entire system, and the center-of-mass
of the system undergoes a slow random walk. If the keyword {zerosum}
is set to {yes}, the total random force is set exactly to zero
by subtracting off an equal part of it from each atom in the group.
As a result, the center-of-mass of a system with zero initial momentum
will not drift over time.
[Restart, fix_modify, output, run start/stop, minimize info:]
No information about this fix is written to "binary restart
@ -186,7 +200,8 @@ dpd/tstat"_pair_dpd.html
[Default:]
The option defaults are scale = 1.0 for all types and tally = no.
The option defaults are scale = 1.0 for all types, tally = no,
zerosum = yes.
:line