forked from lijiext/lammps
126 lines
5.1 KiB
Plaintext
Executable File
126 lines
5.1 KiB
Plaintext
Executable File
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
|
|
|
|
:link(lws,http://lammps.sandia.gov)
|
|
:link(ld,Manual.html)
|
|
:link(lc,Section_commands.html#comm)
|
|
|
|
:line
|
|
|
|
fix nvt/sphere command :h3
|
|
|
|
[Syntax:]
|
|
|
|
fix ID group-ID nvt/sphere keyword value ... :pre
|
|
|
|
ID, group-ID are documented in "fix"_fix.html command
|
|
nvt/sphere = style name of this fix command
|
|
additional thermostat related keyword/value pairs from the "fix nvt"_fix_nh.html command can be appended :ul
|
|
|
|
[Examples:]
|
|
|
|
fix 1 all nvt/sphere temp 300.0 300.0 100.0
|
|
fix 1 all nvt/sphere temp 300.0 300.0 100.0 drag 0.2 :pre
|
|
|
|
[Description:]
|
|
|
|
Perform constant NVT integration to update position, velocity, and
|
|
angular velocity each timestep for extended spherical 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.
|
|
|
|
This fix differs from the "fix nvt"_fix_nh.html command, which
|
|
assumes point particles and only updates their position and velocity.
|
|
|
|
The thermostat is applied to both the translational and rotational
|
|
degrees of freedom for the spherical particles, assuming a compute is
|
|
used which calculates a temperature that includes the rotational
|
|
degrees of freedom (see below). The translational degrees of freedom
|
|
can also have a bias velocity removed from them before thermostatting
|
|
takes place; see the description below.
|
|
|
|
Additional parameters affecting the thermostat are specified by
|
|
keywords and values documented with the "fix nvt"_fix_nh.html
|
|
command. See, for example, discussion of the {temp} and {drag}
|
|
keywords.
|
|
|
|
This fix computes a temperature each timestep. To do this, the fix
|
|
creates its own compute of style "temp/sphere", as if this command
|
|
had been issued:
|
|
|
|
compute fix-ID_temp group-ID temp/sphere :pre
|
|
|
|
See the "compute temp/sphere"_compute_temp_sphere.html command for
|
|
details. Note that the ID of the new compute is the fix-ID +
|
|
underscore + "temp", and the group for the new compute is the same as
|
|
the fix group.
|
|
|
|
Note that this is NOT the compute used by thermodynamic output (see
|
|
the "thermo_style"_thermo_style.html command) with ID = {thermo_temp}.
|
|
This means you can change the attributes of this fix's temperature
|
|
(e.g. its degrees-of-freedom) via the
|
|
"compute_modify"_compute_modify.html command or print this temperature
|
|
during thermodynamic output via the "thermo_style
|
|
custom"_thermo_style.html command using the appropriate compute-ID.
|
|
It also means that changing attributes of {thermo_temp} will have no
|
|
effect on this fix.
|
|
|
|
Like other fixes that perform thermostatting, this fix can be used
|
|
with "compute commands"_compute.html that calculate a temperature
|
|
after removing a "bias" from the atom velocities. E.g. removing the
|
|
center-of-mass velocity from a group of atoms or only calculating
|
|
temperature on the x-component of velocity or only calculating
|
|
temperature for atoms in a geometric region. This is not done by
|
|
default, but only if the "fix_modify"_fix_modify.html command is used
|
|
to assign a temperature compute to this fix that includes such a bias
|
|
term. See the doc pages for individual "compute
|
|
commands"_compute.html to determine which ones include a bias. In
|
|
this case, the thermostat works in the following manner: the current
|
|
temperature is calculated taking the bias into account, bias is
|
|
removed from each atom, thermostatting is performed on the remaining
|
|
thermal degrees of freedom, and the bias is added back in.
|
|
|
|
[Restart, fix_modify, output, run start/stop, minimize info:]
|
|
|
|
This fix writes the state of the Nose/Hoover thermostat to "binary
|
|
restart files"_restart.html. See the "read_restart"_read_restart.html
|
|
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.
|
|
|
|
The "fix_modify"_fix_modify.html {temp} option is supported by this
|
|
fix. You can use it to assign a "compute"_compute.html you have
|
|
defined to this fix which will be used in its thermostatting
|
|
procedure.
|
|
|
|
The "fix_modify"_fix_modify.html {energy} option is supported by this
|
|
fix to add the energy change induced by Nose/Hoover thermostatting to
|
|
the system's potential energy as part of "thermodynamic
|
|
output"_thermo_style.html.
|
|
|
|
This fix computes the same global scalar and global vector of
|
|
quantities as does the "fix nvt"_fix_nh.html command.
|
|
|
|
This fix can ramp its target temperature over multiple runs, using the
|
|
{start} and {stop} keywords of the "run"_run.html command. See the
|
|
"run"_run.html command for details of how to do this.
|
|
|
|
This fix is not invoked during "energy minimization"_minimize.html.
|
|
|
|
[Restrictions:]
|
|
|
|
This fix requires that atoms store torque and angular velocity (omega)
|
|
as defined by the "atom_style"_atom_style.html. It also require they
|
|
store either a per-particle radius or per-type "shape"_shape.html.
|
|
|
|
All particles in the group must be finite-size spheres. They cannot
|
|
be point particles, nor can they be aspherical.
|
|
|
|
[Related commands:]
|
|
|
|
"fix nvt"_fix_nh.html, "fix nve_sphere"_fix_nve_sphere.html, "fix
|
|
nvt_asphere"_fix_nvt_asphere.html, "fix
|
|
npt_sphere"_fix_npt_sphere.html, "fix_modify"_fix_modify.html
|
|
|
|
[Default:] none
|