# compute temp/rotate command

## Syntax

``` LAMMPS
compute ID group-ID temp/rotate
```

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

## Examples

``` LAMMPS
compute Tbead bead temp/rotate
```

## Description

Define a computation that calculates the temperature of a group of
atoms, after subtracting out the center-of-mass velocity and angular
velocity of the group. This is useful if the group is expected to have a
non-zero net velocity and/or global rotation motion for some reason. 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)).

After the center-of-mass velocity and angular velocity has been
subtracted from each atom, the temperature is calculated by the formula

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

where KE is the 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.

The removal of the center-of-mass velocity and angular velocity 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),
[fix temp/rescale](fix_temp_rescale), [fix
temp/berendsen](fix_temp_berendsen), and [fix langevin](fix_langevin).

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.

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

## 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 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

This compute is part of the EXTRA-COMPUTE package. It is only enabled if
LAMMPS was built with that package. See the [Build
package](Build_package) page for more info.

## Related commands

[compute temp](compute_temp)

## Default

none