forked from lijiext/lammps
160 lines
7.1 KiB
HTML
160 lines
7.1 KiB
HTML
<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 nph/asphere command
|
|
</H3>
|
|
<H3>fix nph/asphere/omp command
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>fix ID group-ID nph/asphere args keyword value ...
|
|
</PRE>
|
|
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
|
|
<LI>nph/asphere = style name of this fix command
|
|
<LI>additional barostat related keyword/value pairs from the <A HREF = "fix_nh.html">fix nph</A> command can be appended
|
|
</UL>
|
|
<P><B>Examples:</B>
|
|
</P>
|
|
<PRE>fix 1 all nph/asphere iso 0.0 0.0 1000.0
|
|
fix 2 all nph/asphere x 5.0 5.0 1000.0
|
|
fix 2 all nph/asphere x 5.0 5.0 1000.0 drag 0.2
|
|
fix 2 water nph/asphere aniso 0.0 0.0 1000.0 dilate partial
|
|
</PRE>
|
|
<P><B>Description:</B>
|
|
</P>
|
|
<P>Perform constant NPH integration to update position, velocity,
|
|
orientation, and angular velocity each timestep for aspherical or
|
|
ellipsoidal particles in the group using a Nose/Hoover pressure
|
|
barostat. P is pressure; H is enthalpy. This creates a system
|
|
trajectory consistent with the isenthalpic ensemble.
|
|
</P>
|
|
<P>This fix differs from the <A HREF = "fix_nh.html">fix nph</A> command, which assumes
|
|
point particles and only updates their position and velocity.
|
|
</P>
|
|
<P>Additional parameters affecting the barostat are specified by keywords
|
|
and values documented with the <A HREF = "fix_nh.html">fix nph</A> command. See,
|
|
for example, discussion of the <I>aniso</I>, and <I>dilate</I> keywords.
|
|
</P>
|
|
<P>The particles in the fix group are the only ones whose velocities and
|
|
positions are updated by the velocity/position update portion of the
|
|
NPH integration.
|
|
</P>
|
|
<P>Regardless of what particles are in the fix group, a global pressure is
|
|
computed for all particles. Similarly, when the size of the simulation
|
|
box is changed, all particles are re-scaled to new positions, unless the
|
|
keyword <I>dilate</I> is specified with a value of <I>partial</I>, in which case
|
|
only the particles in the fix group are re-scaled. The latter can be
|
|
useful for leaving the coordinates of particles in a solid substrate
|
|
unchanged and controlling the pressure of a surrounding fluid.
|
|
</P>
|
|
<HR>
|
|
|
|
<P>This fix computes a temperature and pressure each timestep. To do
|
|
this, the fix creates its own computes of style "temp/asphere" and
|
|
"pressure", as if these commands had been issued:
|
|
</P>
|
|
<PRE>compute fix-ID_temp all temp/asphere
|
|
compute fix-ID_press all pressure fix-ID_temp
|
|
</PRE>
|
|
<P>See the <A HREF = "compute_temp_asphere.html">compute temp/asphere</A> and <A HREF = "compute_pressure.html">compute
|
|
pressure</A> commands for details. Note that the
|
|
IDs of the new computes are the fix-ID + underscore + "temp" or fix_ID
|
|
+ underscore + "press", and the group for the new computes is "all"
|
|
since pressure is computed for the entire system.
|
|
</P>
|
|
<P>Note that these are NOT the computes used by thermodynamic output (see
|
|
the <A HREF = "thermo_style.html">thermo_style</A> command) with ID = <I>thermo_temp</I>
|
|
and <I>thermo_press</I>. This means you can change the attributes of this
|
|
fix's temperature or pressure via the
|
|
<A HREF = "compute_modify.html">compute_modify</A> command or print this temperature
|
|
or pressure during thermodynamic 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> or
|
|
<I>thermo_press</I> will have no effect on this fix.
|
|
</P>
|
|
<HR>
|
|
|
|
<P>Styles with a <I>cuda</I>, <I>gpu</I>, <I>intel</I>, <I>kk</I>, <I>omp</I>, or <I>opt</I> suffix are
|
|
functionally the same as the corresponding style without the suffix.
|
|
They have been optimized to run faster, depending on your available
|
|
hardware, as discussed in <A HREF = "Section_accelerate.html">Section_accelerate</A>
|
|
of the manual. The accelerated styles take the same arguments and
|
|
should produce the same results, except for round-off and precision
|
|
issues.
|
|
</P>
|
|
<P>These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
|
|
KOKKOS, USER-OMP and OPT packages, respectively. They are only
|
|
enabled if LAMMPS was built with those packages. See the <A HREF = "Section_start.html#start_3">Making
|
|
LAMMPS</A> section for more info.
|
|
</P>
|
|
<P>You can specify the accelerated styles explicitly in your input script
|
|
by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
|
|
switch</A> when you invoke LAMMPS, or you can
|
|
use the <A HREF = "suffix.html">suffix</A> command in your input script.
|
|
</P>
|
|
<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
|
|
more instructions on how to use the accelerated styles effectively.
|
|
</P>
|
|
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
|
|
</P>
|
|
<P>This fix writes the state of the Nose/Hoover barostat to <A HREF = "restart.html">binary
|
|
restart files</A>. See the <A HREF = "read_restart.html">read_restart</A>
|
|
command for info on how to re-specify a fix in an input script that
|
|
reads a restart file, so that the operation of the fix continues in an
|
|
uninterrupted fashion.
|
|
</P>
|
|
<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>temp</I> and <I>press</I> options are
|
|
supported by this fix. You can use them to assign a
|
|
<A HREF = "compute.html">compute</A> you have defined to this fix which will be used
|
|
in its thermostatting or barostatting procedure. If you do this, note
|
|
that the kinetic energy derived from the compute temperature should be
|
|
consistent with the virial term computed using all atoms for the
|
|
pressure. LAMMPS will warn you if you choose to compute temperature
|
|
on a subset of atoms.
|
|
</P>
|
|
<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>energy</I> option is supported by this
|
|
fix to add the energy change induced by Nose/Hoover barostatting to
|
|
the system's potential energy as part of <A HREF = "thermo_style.html">thermodynamic
|
|
output</A>.
|
|
</P>
|
|
<P>This fix computes the same global scalar and global vector of
|
|
quantities as does the <A HREF = "fix_nh.html">fix nph</A> command.
|
|
</P>
|
|
<P>This fix can ramp its target pressure over multiple runs, using the
|
|
<I>start</I> and <I>stop</I> keywords of the <A HREF = "run.html">run</A> command. See the
|
|
<A HREF = "run.html">run</A> command for details of how to do this.
|
|
</P>
|
|
<P>This fix is not invoked during <A HREF = "minimize.html">energy minimization</A>.
|
|
</P>
|
|
<P><B>Restrictions:</B>
|
|
</P>
|
|
<P>This fix is part of the ASPHERE package. It is only enabled if LAMMPS
|
|
was built with that package. See the <A HREF = "Section_start.html#start_3">Making
|
|
LAMMPS</A> section for more info.
|
|
</P>
|
|
<P>This fix requires that atoms store torque and angular momementum and a
|
|
quaternion as defined by the <A HREF = "atom_style.html">atom_style ellipsoid</A>
|
|
command.
|
|
</P>
|
|
<P>All particles in the group must be finite-size. They cannot be point
|
|
particles, but they can be aspherical or spherical as defined by their
|
|
shape attribute.
|
|
</P>
|
|
<P><B>Related commands:</B>
|
|
</P>
|
|
<P><A HREF = "fix_nh.html">fix nph</A>, <A HREF = "fix_nve_asphere.html">fix nve_asphere</A>, <A HREF = "fix_nvt_asphere.html">fix
|
|
nvt_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> none
|
|
</P>
|
|
</HTML>
|