forked from lijiext/lammps
150 lines
6.6 KiB
Plaintext
150 lines
6.6 KiB
Plaintext
"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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compute command :h3
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[Syntax:]
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compute ID group-ID style args :pre
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ID = user-assigned name for the computation
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group-ID = ID of the group of atoms to perform the computation on
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style = one of a list of possible style names (see below)
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args = arguments used by a particular style :ul
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[Examples:]
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compute 1 all temp
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compute newtemp flow temp/partial 1 1 0
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compute 3 all ke/atom :pre
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[Description:]
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Create a computation that will be performed on a group of atoms.
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Quantities calculated by a compute are instantaneous values, meaning
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they are calculated from information about atoms on the current
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timestep or iteration. There are two kinds of computes, "global"
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computes that calculate one or more values for the entire group of
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atoms, and "per-atom" computes that calculate one or more values for
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each atom in the group. The latter has the word "atom" in its style
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name.
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In LAMMPS, a "compute" can be used in several ways. The results of
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global computes can be output via the "thermo_style
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custom"_thermo_style.html or "fix ave/time"_fix_ave_time.html command.
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Or the values can be referenced in a "variable equal"_variable.html or
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"variable atom"_variable.html command. The results of computes that
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calculate a global temperature or pressure can be used by fixes that
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do thermostatting or barostatting and when atom velocities are
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created.
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The results of per-atom computes can be output via the "dump
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custom"_dump.html command or the "fix
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ave/spatial"_fix_ave_spatial.html command. Or the per-atom values can
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be time-averaged via the "fix ave/atom"_fix_ave_atom.html command and
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then output via the "dump custom"_dump.html or "fix
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ave/spatial"_fix_ave_spatial.html commands. Or the per-atom values
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can be referenced in a "variable atom"_variable.html command. Note
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that the value of per-atom computes will be 0.0 for atoms not in the
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specified compute group.
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See this "howto section"_Section_howto.html#4_15 for a summary of
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various LAMMPS output options, many of which involve computes.
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The ID of a compute can only contain alphanumeric characters and
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underscores.
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The results of computes that calculate global quantities can be either
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"intensive" or "extensive" values. Intensive means the value is
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independent of the number of atoms in the simulation,
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e.g. temperature. Extensive means the value scales with the number of
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atoms in the simulation, e.g. total rotational kinetic energy.
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"Thermodynamic output"_thermo_style.html will normalize extensive
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values depending on the "thermo_modify norm" setting. But if a
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compute value is accessed in another way, e.g. by a
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"variable"_variable.html, you may need to know whether it is an
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intensive or extensive value. See the doc page for individual
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computes for further info.
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LAMMPS creates its own global computes for thermodynamic output.
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Three computes are always created, named "thermo_temp",
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"thermo_press", and "thermo_pe", as if these commands had been invoked
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in the input script:
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compute thermo_temp all temp
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compute thermo_press all pressure thermo_temp
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compute thermo_pe all pe :pre
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Additional computes for other quantities are created if the thermo
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style requires it. See the documentation for the
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"thermo_style"_thermo_style.html command.
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Fixes that calculate temperature or pressure, i.e. for thermostatting
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or barostatting, may also create computes. These are discussed in the
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documentation for specific "fix"_fix.html commands.
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In all these cases, the default computes can be replaced by computes
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defined by the user in the input script, as described by the
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"thermo_modify"_thermo_modify.html and "fix modify"_fix_modify.html
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commands.
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Properties of either a default or user-defined compute can be modified
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via the "compute_modify"_compute_modify.html command.
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Computes can be deleted with the "uncompute"_uncompute.html command.
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Code for new computes can be added to LAMMPS (see "this
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section"_Section_modify.html of the manual) and the results of their
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calculations accessed in the various ways described above.
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Each compute style has its own doc page which describes its arguments
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and what it does. Here is an alphabetic list of compute styles
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available in LAMMPS:
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"centro/atom"_compute_centro_atom.html - centro-symmetry parameter for each atom
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"cna/atom"_compute_cna_atom.html - common neighbor analysis (CNA) for each atom
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"coord/atom"_compute_coord_atom.html - coordination number for each atom
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"damage/atom"_compute_damage_atom.html - Peridynamic damage for each atom
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"displace/atom"_compute_displace_atom.html - displacement of each atom
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"erotate/asphere"_compute_erotate_asphere.html - rotational energy of aspherical particles
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"erotate/sphere"_compute_erotate_sphere.html - rotational energy of spherical particles
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"group/group"_compute_group_group.html - energy/force between two groups of atoms
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"heat/flux"_compute_heat_flux.html - heat flux through a group of atoms
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"ke"_compute_ke.html - translational kinetic energy
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"ke/atom"_compute_ke_atom.html - kinetic energy for each atom
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"pe"_compute_pe.html - potential energy
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"pe/atom"_compute_pe_atom.html - potential energy for each atom
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"pressure"_compute_pressure.html - total pressure and pressure tensor
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"reduce"_compute_reduce.html - combine per-atom quantities into a single global value
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"reduce/region"_compute_reduce.html - same as compute reduce, within a region
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"stress/atom"_compute_stress_atom.html - stress tensor for each atom
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"temp"_compute_temp.html - temperature of group of atoms
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"temp/asphere"_compute_temp_asphere.html - temperature of aspherical particles
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"temp/com"_compute_temp_com.html - temperature after subtracting center-of-mass velocity
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"temp/deform"_compute_temp_deform.html - temperature excluding box deformation velocity
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"temp/partial"_compute_temp_partial.html - temperature excluding one or more dimensions of velocity
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"temp/profile"_compute_temp_profile.html - temperature excluding a binned velocity profile
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"temp/ramp"_compute_temp_ramp.html - temperature excluding ramped velocity component
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"temp/region"_compute_temp_region.html - temperature of a region of atoms
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"temp/sphere"_compute_temp_sphere.html - temperature of spherical particles :ul
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There are also additional compute styles submitted by users which are
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included in the LAMMPS distribution. The list of these with links to
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the individual styles are given in the compute section of "this
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page"_Section_commands.html#3_5.
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[Restrictions:] none
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[Related commands:]
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"uncompute"_uncompute.html, "compute_modify"_compute_modify.html, "fix
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ave/atom"_fix_ave_atom.html, "fix ave/spatial"_fix_ave_spatial.html,
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"fix ave/time"_fix_ave_time.html
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[Default:] none
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