lammps/doc/compute_temp_partial.txt

"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)

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compute temp/partial command :h3
compute temp/partial/cuda command :h3

[Syntax:]

compute ID group-ID temp/partial xflag yflag zflag :pre

ID, group-ID are documented in "compute"_compute.html command
temp/partial = style name of this compute command
xflag,yflag,zflag = 0/1 for whether to exclude/include this dimension :ul

[Examples:]

compute newT flow temp/partial 1 1 0 :pre

[Description:]

Define a computation that calculates the temperature of a group of
atoms, after excluding one or more velocity components.  A compute of
this style can be used by any command that computes a temperature,
e.g. "thermo_modify"_thermo_modify.html, "fix
temp/rescale"_fix_temp_rescale.html, "fix npt"_fix_nh.html, etc.

The temperature is calculated by the formula KE = dim/2 N k T, where
KE = total kinetic energy of the group of atoms (sum of 1/2 m v^2),
dim = dimensionality of the simulation, N = number of atoms in the
group, k = Boltzmann constant, and T = temperature.  The calculation
of KE excludes the x, y, or z dimensions if xflag, yflag, or zflag =
0.  The dim parameter is adjusted to give the correct number of
degrees of freedom.

A kinetic energy tensor, stored as a 6-element vector, is also
calculated by this compute for use in the calculation of a pressure
tensor.  The formula for the components of the tensor is the same as
the above formula, except that v^2 is replaced by vx*vy for the xy
component, etc.  The 6 components of the vector are ordered xx, yy,
zz, xy, xz, yz.

The number of atoms contributing to the temperature is assumed to be
constant for the duration of the run; use the {dynamic} option of the
"compute_modify"_compute_modify.html command if this is not the case.

The removal of velocity components by this fix is essentially
computing the temperature after a "bias" has been removed from the
velocity of the atoms.  If this compute is used with a fix command
that performs thermostatting then this bias will be subtracted from
each atom, thermostatting of the remaining thermal velocity will be
performed, and the bias will be added back in.  Thermostatting fixes
that work in this way include "fix nvt"_fix_nh.html, "fix
temp/rescale"_fix_temp_rescale.html, "fix
temp/berendsen"_fix_temp_berendsen.html, and "fix
langevin"_fix_langevin.html.

This compute subtracts out degrees-of-freedom due to fixes that
constrain molecular motion, such as "fix shake"_fix_shake.html and
"fix rigid"_fix_rigid.html.  This means the temperature of groups of
atoms that include these constraints will be computed correctly.  If
needed, the subtracted degrees-of-freedom can be altered using the
{extra} option of the "compute_modify"_compute_modify.html command.

See "this howto section"_Section_howto.html#4_16 of the manual for a
discussion of different ways to compute temperature and perform
thermostatting.

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Styles with a {cuda} 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
"this section"_Section_accelerate.html of the manual.  The accelerated
styles take the same arguments and should produce the same results,
except for round-off and precision issues.

These accelerated styles are part of the "user-cuda" package.  They
are only enabled if LAMMPS was built with that package.  See the
"Making LAMMPS"_Section_start.html#2_3 section for more info.

You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the "-suffix command-line
switch"_Section_start.html#2_6 when you invoke LAMMPS, or you can use
the "suffix"_suffix.html command in your input script.

See "this section"_Section_accelerate.html of the manual for more
instructions on how to use the accelerated styles effectively.

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[Output info:]

This compute calculates a global scalar (the temperature) and a global
vector of length 6 (KE tensor), which can be accessed by indices 1-6.
These values can be used by any command that uses global scalar or
vector values from a compute as input.  See "this
section"_Section_howto.html#4_15 for an overview of LAMMPS output
options.

The scalar value calculated by this compute is "intensive".  The
vector values are "extensive".

The scalar value will be in temperature "units"_units.html.  The
vector values will be in energy "units"_units.html.

[Restrictions:] none

[Related commands:]

"compute temp"_compute_temp.html, "compute
temp/region"_compute_temp_region.html, "compute
pressure"_compute_pressure.html

[Default:] none