# fix nve/spin command

## Syntax

    fix ID group-ID nve/spin keyword values

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

-   nve/spin = style name of this fix command

-   keyword = *lattice*

        *lattice* value = *moving* or *frozen*
          moving = integrate both spin and atomic degress of freedom
          frozen = integrate spins on a fixed lattice

## Examples

``` LAMMPS
fix 3 all nve/spin lattice moving
fix 1 all nve/spin lattice frozen
```

## Description

Perform a symplectic integration for the spin or spin-lattice system.

The *lattice* keyword defines if the spins are integrated on a lattice
of fixed atoms (lattice = frozen), or if atoms are moving (lattice =
moving). The first case corresponds to a spin dynamics calculation, and
the second to a spin-lattice calculation. By default a spin-lattice
integration is performed (lattice = moving).

The *nve/spin* fix applies a Suzuki-Trotter decomposition to the
equations of motion of the spin lattice system, following the scheme:

![image](JPG/fix_integration_spin_stdecomposition.jpg){.align-center}

according to the implementation reported in [(Omelyan)](Omelyan1).

A sectoring method enables this scheme for parallel calculations. The
implementation of this sectoring algorithm is reported in
[(Tranchida)](Tranchida1).

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

## Restrictions

This fix style can only be used if LAMMPS was built with the SPIN
package. See the [Build package](Build_package) page for more info.

To use the spin algorithm, it is necessary to define a map with the
atom_modify command. Typically, by adding the command:

``` LAMMPS
atom_modify map array
```

before you create the simulation box. Note that the keyword \"hash\"
instead of \"array\" is also valid.

## Related commands

[atom_style spin](atom_style), [fix nve](fix_nve)

## Default

The option default is lattice = moving.

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

::: {#Omelyan1}
**(Omelyan)** Omelyan, Mryglod, and Folk. Phys. Rev. Lett. 86(5), 898.
(2001).
:::

::: {#Tranchida1}
**(Tranchida)** Tranchida, Plimpton, Thibaudeau and Thompson, Journal of
Computational Physics, 372, 406-425, (2018).
:::