# fix nve/sphere command

Accelerator Variants: *nve/sphere/omp*, *nve/sphere/kk*

## Syntax

    fix ID group-ID nve/sphere

-   ID, group-ID are documented in [fix](fix) command

-   nve/sphere = style name of this fix command

-   zero or more keyword/value pairs may be appended

-   keyword = *update* or *disc*

        *update* value = *dipole* or *dipole/dlm*
          dipole = update orientation of dipole moment during integration
          dipole/dlm = use DLM integrator to update dipole orientation
        *disc* value = none = treat particles as 2d discs, not spheres

## Examples

``` LAMMPS
fix 1 all nve/sphere
fix 1 all nve/sphere update dipole
fix 1 all nve/sphere disc
fix 1 all nve/sphere update dipole/dlm
```

## Description

Perform constant NVE integration to update position, velocity, and
angular velocity for finite-size spherical particles in the group each
timestep. V is volume; E is energy. This creates a system trajectory
consistent with the microcanonical ensemble.

This fix differs from the [fix nve](fix_nve) command, which assumes
point particles and only updates their position and velocity.

If the *update* keyword is used with the *dipole* value, then the
orientation of the dipole moment of each particle is also updated during
the time integration. This option should be used for models where a
dipole moment is assigned to finite-size particles, e.g. spheroids via
use of the [atom_style hybrid sphere dipole](atom_style) command.

The default dipole orientation integrator can be changed to the
Dullweber-Leimkuhler-McLachlan integration scheme
[(Dullweber)](nh-Dullweber) when using *update* with the value
*dipole/dlm*. This integrator is symplectic and time-reversible, giving
better energy conservation and allows slightly longer timesteps at only
a small additional computational cost.

If the *disc* keyword is used, then each particle is treated as a 2d
disc (circle) instead of as a sphere. This is only possible for 2d
simulations, as defined by the [dimension](dimension) keyword. The only
difference between discs and spheres in this context is their moment of
inertia, as used in the time integration.

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

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.

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

## Restart, fix_modify, output, run start/stop, minimize info

No information about this fix is written to [binary restart
files](restart). None of the [fix_modify](fix_modify) options are
relevant to this fix. No global or per-atom quantities are stored by
this fix for access by various [output commands](Howto_output). No
parameter of this fix can be used with the *start/stop* keywords of the
[run](run) command. This fix is not invoked during [energy
minimization](minimize).

## Restrictions

This fix requires that atoms store torque and angular velocity (omega)
and a radius as defined by the [atom_style sphere](atom_style) command.
If the *dipole* keyword is used, then they must also store a dipole
moment as defined by the [atom_style dipole](atom_style) command.

All particles in the group must be finite-size spheres. They cannot be
point particles.

Use of the *disc* keyword is only allowed for 2d simulations, as defined
by the [dimension](dimension) keyword.

## Related commands

[fix nve](fix_nve), [fix nve/asphere](fix_nve_asphere)

## Default

none

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::: {#nve-Dullweber}
**(Dullweber)** Dullweber, Leimkuhler and McLachlan, J Chem Phys, 107,
5840 (1997).
:::