forked from lijiext/lammps
113 lines
4.0 KiB
Plaintext
113 lines
4.0 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,Commands_all.html)
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:line
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compute temp command :h3
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compute temp/kk command :h3
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[Syntax:]
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compute ID group-ID temp :pre
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ID, group-ID are documented in "compute"_compute.html command
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temp = style name of this compute command :ul
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[Examples:]
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compute 1 all temp
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compute myTemp mobile temp :pre
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[Description:]
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Define a computation that calculates the temperature of a group of
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atoms. A compute of this style can be used by any command that
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computes a temperature, e.g. "thermo_modify"_thermo_modify.html, "fix
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temp/rescale"_fix_temp_rescale.html, "fix npt"_fix_nh.html, etc.
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The temperature is calculated by the formula KE = dim/2 N k T, where
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KE = total kinetic energy of the group of atoms (sum of 1/2 m v^2),
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dim = 2 or 3 = dimensionality of the simulation, N = number of atoms
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in the group, k = Boltzmann constant, and T = temperature.
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A kinetic energy tensor, stored as a 6-element vector, is also
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calculated by this compute for use in the computation of a pressure
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tensor. The formula for the components of the tensor is the same as
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the above formula, except that v^2 is replaced by vx*vy for the xy
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component, etc. The 6 components of the vector are ordered xx, yy,
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zz, xy, xz, yz.
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The number of atoms contributing to the temperature is assumed to be
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constant for the duration of the run; use the {dynamic} option of the
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"compute_modify"_compute_modify.html command if this is not the case.
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This compute subtracts out degrees-of-freedom due to fixes that
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constrain molecular motion, such as "fix shake"_fix_shake.html and
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"fix rigid"_fix_rigid.html. This means the temperature of groups of
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atoms that include these constraints will be computed correctly. If
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needed, the subtracted degrees-of-freedom can be altered using the
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{extra} option of the "compute_modify"_compute_modify.html command.
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A compute of this style with the ID of "thermo_temp" is created when
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LAMMPS starts up, as if this command were in the input script:
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compute thermo_temp all temp :pre
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See the "thermo_style" command for more details.
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See the "Howto thermostat"_Howto_thermostat.html doc page for a
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discussion of different ways to compute temperature and perform
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thermostatting.
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:line
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Styles with a {gpu}, {intel}, {kk}, {omp}, or {opt} suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed on the "Speed packages"_Speed_packages.html doc
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page. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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LAMMPS was built with those packages. See the "Build
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package"_Build_package.html doc page for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the "-suffix command-line
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switch"_Run_options.html when you invoke LAMMPS, or you can use the
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"suffix"_suffix.html command in your input script.
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See the "Speed packages"_Speed_packages.html doc page for more
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instructions on how to use the accelerated styles effectively.
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:line
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[Output info:]
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This compute calculates a global scalar (the temperature) and a global
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vector of length 6 (KE tensor), which can be accessed by indices 1-6.
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These values can be used by any command that uses global scalar or
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vector values from a compute as input. See the "Howto
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output"_Howto_output.html doc page for an overview of LAMMPS output
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options.
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The scalar value calculated by this compute is "intensive". The
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vector values are "extensive".
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The scalar value will be in temperature "units"_units.html. The
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vector values will be in energy "units"_units.html.
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[Restrictions:] none
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[Related commands:]
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"compute temp/partial"_compute_temp_partial.html, "compute
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temp/region"_compute_temp_region.html, "compute
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pressure"_compute_pressure.html
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[Default:] none
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