# compute erotate/sphere command

Accelerator Variants: *erotate/sphere/kk*

## Syntax

``` LAMMPS
compute ID group-ID erotate/sphere
```

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

## Examples

``` LAMMPS
compute 1 all erotate/sphere
```

## Description

Define a computation that calculates the rotational kinetic energy of a
group of spherical particles.

The rotational energy is computed as $\frac12 I \omega^2$, where $I$ is
the moment of inertia for a sphere and $\omega$ is the particle\'s
angular velocity.

:::: note
::: title
Note
:::

For [2d models](dimension), particles are treated as spheres, not disks,
meaning their moment of inertia will be the same as in 3d.
::::

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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 KE). This value can be used
by any command that uses a global scalar value 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 \"extensive\". The scalar
value will be in energy [units](units).

## Restrictions

This compute requires that atoms store a radius and angular velocity
(omega) as defined by the [atom_style sphere](atom_style) command.

All particles in the group must be finite-size spheres or point
particles. They cannot be aspherical. Point particles will not
contribute to the rotational energy.

## Related commands

[compute erotate/asphere](compute_erotate_asphere)

## Default

none