forked from lijiext/lammps
125 lines
5.1 KiB
Plaintext
125 lines
5.1 KiB
Plaintext
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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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fix nph/asphere command :h3
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[Syntax:]
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fix ID group-ID nph/asphere args keyword value ... :pre
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ID, group-ID are documented in "fix"_fix.html command
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nph/asphere = style name of this fix command
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additional barostat related keyword/value pairs from the "fix nph"_fix_nh.html command can be appended :ul
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[Examples:]
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fix 1 all nph/asphere iso 0.0 0.0 1000.0
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fix 2 all nph/asphere x 5.0 5.0 1000.0
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fix 2 all nph/asphere x 5.0 5.0 1000.0 drag 0.2
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fix 2 water nph/asphere aniso 0.0 0.0 1000.0 dilate partial :pre
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[Description:]
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Perform constant NPH integration to update position, velocity,
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orientation, and angular velocity each timestep for aspherical or
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ellipsoidal particles in the group using a Nose/Hoover pressure
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barostat. P is pressure; H is enthalpy. This creates a system
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trajectory consistent with the isenthalpic ensemble.
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This fix differs from the "fix nph"_fix_nh.html command, which assumes
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point particles and only updates their position and velocity.
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Additional parameters affecting the barostat are specified by keywords
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and values documented with the "fix nph"_fix_nh.html command. See,
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for example, discussion of the {aniso}, and {dilate} keywords.
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The particles in the fix group are the only ones whose velocities and
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positions are updated by the velocity/position update portion of the
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NPH integration.
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Regardless of what particles are in the fix group, a global pressure is
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computed for all particles. Similarly, when the size of the simulation
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box is changed, all particles are re-scaled to new positions, unless the
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keyword {dilate} is specified with a value of {partial}, in which case
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only the particles in the fix group are re-scaled. The latter can be
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useful for leaving the coordinates of particles in a solid substrate
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unchanged and controlling the pressure of a surrounding fluid.
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:line
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This fix computes a temperature and pressure each timestep. To do
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this, the fix creates its own computes of style "temp/asphere" and
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"pressure", as if these commands had been issued:
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compute fix-ID_temp all temp/asphere
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compute fix-ID_press all pressure fix-ID_temp :pre
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See the "compute temp/asphere"_compute_temp_asphere.html and "compute
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pressure"_compute_pressure.html commands for details. Note that the
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IDs of the new computes are the fix-ID + underscore + "temp" or fix_ID
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+ underscore + "press", and the group for the new computes is "all"
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since pressure is computed for the entire system.
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Note that these are NOT the computes used by thermodynamic output (see
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the "thermo_style"_thermo_style.html command) with ID = {thermo_temp}
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and {thermo_press}. This means you can change the attributes of this
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fix's temperature or pressure via the
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"compute_modify"_compute_modify.html command or print this temperature
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or pressure during thermodynamic output via the "thermo_style
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custom"_thermo_style.html command using the appropriate compute-ID.
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It also means that changing attributes of {thermo_temp} or
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{thermo_press} will have no effect on this fix.
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[Restart, fix_modify, output, run start/stop, minimize info:]
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This fix writes the state of the Nose/Hoover barostat to "binary
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restart files"_restart.html. See the "read_restart"_read_restart.html
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command for info on how to re-specify a fix in an input script that
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reads a restart file, so that the operation of the fix continues in an
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uninterrupted fashion.
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The "fix_modify"_fix_modify.html {temp} and {press} options are
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supported by this fix. You can use them to assign a
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"compute"_compute.html you have defined to this fix which will be used
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in its thermostatting or barostatting procedure. If you do this, note
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that the kinetic energy derived from the compute temperature should be
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consistent with the virial term computed using all atoms for the
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pressure. LAMMPS will warn you if you choose to compute temperature
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on a subset of atoms.
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The "fix_modify"_fix_modify.html {energy} option is supported by this
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fix to add the energy change induced by Nose/Hoover barostatting to
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the system's potential energy as part of "thermodynamic
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output"_thermo_style.html.
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This fix computes the same global scalar and global vector of
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quantities as does the "fix nph"_fix_nh.html command.
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This fix can ramp its target pressure over multiple runs, using the
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{start} and {stop} keywords of the "run"_run.html command. See the
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"run"_run.html command for details of how to do this.
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This fix is not invoked during "energy minimization"_minimize.html.
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[Restrictions:]
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This fix requires that atoms store torque and angular velocity (omega)
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as defined by the "atom_style"_atom_style.html. It also require they
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store either a per-particle diameter or per-type "shape"_shape.html.
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All particles in the group must be finite-size. They cannot be point
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particles, but they can be aspherical or spherical.
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[Related commands:]
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"fix nph"_fix_nh.html, "fix nve_asphere"_fix_nve_asphere.html, "fix
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nvt_asphere"_fix_nvt_asphere.html, "fix npt_asphere"_fix_npt_asphere.html,
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"fix_modify"_fix_modify.html
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[Default:] none
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