# compute temp command

Accelerator Variants: *temp/kk*

## Syntax

``` LAMMPS
compute ID group-ID temp
```

-   ID, group-ID are documented in [compute](compute) command
-   temp = style name of this compute command

## Examples

``` LAMMPS
compute 1 all temp
compute myTemp mobile temp
```

## Description

Define a computation that calculates the temperature of a group of
atoms. A compute of this style can be used by any command that computes
a temperature, e.g. [thermo_modify](thermo_modify), [fix
temp/rescale](fix_temp_rescale), [fix npt](fix_nh), etc.

The temperature is calculated by the formula

$$\text{KE} = \frac{\text{dim}}{2} N k_B T,$$

where KE = total kinetic energy of the group of atoms (sum of
$\frac12 m v^2$), dim = 2 or 3 is the dimensionality of the simulation,
$N$ is the number of atoms in the group, $k_B$ is the Boltzmann
constant, and $T$ is the absolute temperature.

A kinetic energy tensor, stored as a six-element vector, is also
calculated by this compute for use in the computation 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 $v_x
v_y$ for the $xy$ component, and so on. The six 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) command if this is not the case.

This compute subtracts out degrees-of-freedom due to fixes that
constrain molecular motion, such as [fix shake](fix_shake) and [fix
rigid](fix_rigid). 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) command.

A compute of this style with the ID of \"thermo_temp\" is created when
LAMMPS starts up, as if this command were in the input script:

``` LAMMPS
compute thermo_temp all temp
```

See the \"thermo_style\" command for more details.

See the [Howto thermostat](Howto_thermostat) page for a discussion of
different ways to compute temperature and perform thermostatting.

------------------------------------------------------------------------

Styles with a *gpu*, *intel*, *kk*, *omp*, or *opt* 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 on the [Accelerator packages](Speed_packages)
page. 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 GPU, INTEL, KOKKOS, OPENMP, and
OPT packages, respectively. They are only enabled if LAMMPS was built
with those packages. See the [Build package](Build_package) page 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](Run_options) when you invoke LAMMPS, or you can use the
[suffix](suffix) command in your input script.

See the [Accelerator packages](Speed_packages) page for more
instructions on how to use the accelerated styles effectively.

------------------------------------------------------------------------

## Output info

This compute calculates a global scalar (the temperature) and a global
vector of length six (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 the [Howto
output](Howto_output) page 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). The vector
values will be in energy [units](units).

## Restrictions

> none

## Related commands

[compute temp/partial](compute_temp_partial), [compute
temp/region](compute_temp_region), [compute pressure](compute_pressure)

## Default

none