Page Menu
Home
c4science
Search
Configure Global Search
Log In
Files
F93946584
fix_nvt_asphere.html
No One
Temporary
Actions
Download File
Edit File
Delete File
View Transforms
Subscribe
Mute Notifications
Award Token
Subscribers
None
File Metadata
Details
File Info
Storage
Attached
Created
Mon, Dec 2, 18:13
Size
4 KB
Mime Type
text/html
Expires
Wed, Dec 4, 18:13 (2 d)
Engine
blob
Format
Raw Data
Handle
22685905
Attached To
rLAMMPS lammps
fix_nvt_asphere.html
View Options
<HTML>
<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
<HR>
<H3>fix nvt/asphere command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID nvt/asphere Tstart Tstop Tdamp keyword value ...
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>nvt/asphere = style name of this fix command
<LI>Tstart,Tstop = desired temperature at start/end of run
<LI>Tdamp = temperature damping parameter (time units)
<LI>zero or more keyword/value pairs may be appended to the args
<LI>keyword = <I>drag</I>
<PRE> <I>drag</I> value = drag factor added to thermostat (0.0 = no drag)
</PRE>
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix 1 all nvt/asphere 300.0 300.0 100.0
fix 1 all nvt/asphere 300.0 300.0 100.0 drag 0.2
</PRE>
<P><B>Description:</B>
</P>
<P>Perform constant NVT integration to update positions, velocities,
and angular velocities each timestep for aspherical or ellipsoidal
particles in the group using a Nose/Hoover temperature thermostat.
V is volume; T is temperature. This creates a system trajectory
consistent with the canonical ensemble.
</P>
<P>The desired temperature at each timestep is a ramped value during the
run from <I>Tstart</I> to <I>Tstop</I>. The <A HREF = "run.html">run</A> command documents
how to make the ramping take place across multiple runs. The <I>Tdamp</I>
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 <A HREF = "units.html">units</A> command).
</P>
<P>In some cases (e.g. for solids) the temperature of the system can
oscillate undesirably when a Nose/Hoover thermostat is applied. The
optional <I>drag</I> keyword will damp these oscillations, although it
alters the Nose/Hoover equations. A value of 0.0 (no drag) leaves the
Nose/Hoover formalism unchanged. A non-zero value adds a drag term;
the larger the value specified, the greater the damping effect.
Performing a short run and monitoring the temperature is the best way
to determine if the drag term is working. Typically a value between
0.2 to 2.0 is sufficient to damp oscillations after a few periods.
</P>
<P>This fix computes a temperature each timestep. To do this, the fix
creates its own compute of style "temp/asphere", as if this command
had been issued:
</P>
<PRE>compute fix-ID_temp group-ID temp/asphere
</PRE>
<P>See the <A HREF = "compute_temp_asphere.html">compute temp/asphere</A> command for
details. Note that the ID of the new compute is the fix-ID with
underscore + "temp" appended and the group for the new compute is
the same as the fix group.
</P>
<P>Note that this is NOT the compute used by thermodynamic output (see
the <A HREF = "thermo_style.html">thermo_style</A> command) with ID = <I>thermo_temp</I>.
This means you can change the attributes of this fix's temperature
(e.g. its degrees-of-freedom) via the
<A HREF = "compute_modify.html">compute_modify</A> command or print this temperature
during thermodyanmic output via the <A HREF = "thermo_style.html">thermo_style
custom</A> command using the appropriate compute-ID.
It also means that changing attributes of <I>thermo_temp</I> will have no
effect on this fix. Alternatively, you can directly assign a new
compute (for calculating temeperature) that you have defined to this
fix via the <A HREF = "fix_modify.html">fix_modify</A> command.
</P>
<P>This fix makes a contribution to the potential energy of the system
that can be included in thermodynamic output of potential energy using
the <A HREF = "fix_modify.html">fix_modify energy</A> option. The contribution can
also be printed by itself via the keyword <I>f_fix-ID</I> in the
<A HREF = "thermo_style.html">thermo_style custom</A> command.
</P>
<P><B>Restrictions:</B>
</P>
<P>Can only be used if LAMMPS was built with the "asphere" package.
</P>
<P>The final Tstop cannot be 0.0 since it would make the target T = 0.0
at some timestep during the simulation which is not allowed in
the Nose/Hoover formulation.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix_nvt.html">fix nvt</A>, <A HREF = "fix_nve_asphere.html">fix nve_asphere</A>, <A HREF = "fix_npt_asphere.html">fix
npt_asphere</A>, <A HREF = "fix_modify.html">fix_modify</A>
</P>
<P><B>Default:</B>
</P>
<P>The keyword defaults are drag = 0.0.
</P>
</HTML>
Event Timeline
Log In to Comment