# compute spin command

## Syntax

``` LAMMPS
compute ID group-ID spin
```

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

## Examples

``` LAMMPS
compute out_mag all spin
```

## Description

Define a computation that calculates magnetic quantities for a system of
atoms having spins.

This compute calculates the following 6 magnetic quantities:

-   the three first quantities are the x,y and z coordinates of the
    total magnetization,
-   the fourth quantity is the norm of the total magnetization,
-   The fifth quantity is the magnetic energy (in eV),
-   The sixth one is referred to as the spin temperature, according to
    the work of [(Nurdin)](Nurdin1).

The simplest way to output the results of the compute spin calculation
is to define some of the quantities as variables, and to use the thermo
and thermo_style commands, for example:

``` LAMMPS
compute out_mag         all spin

variable mag_z          equal c_out_mag[3]
variable mag_norm       equal c_out_mag[4]
variable temp_mag       equal c_out_mag[6]

thermo                  10
thermo_style            custom step v_mag_z v_mag_norm v_temp_mag
```

This series of commands evaluates the total magnetization along z, the
norm of the total magnetization, and the magnetic temperature. Three
variables are assigned to those quantities. The thermo and thermo_style
commands print them every 10 timesteps.

## Output info

The array values are \"intensive\". The array values will be in metal
units ([units](units)).

## Restrictions

The *spin* compute is part of the SPIN package. This compute is only
enabled if LAMMPS was built with this package. See the [Build
package](Build_package) page for more info. The atom_style has to be
\"spin\" for this compute to be valid.

**Related commands:**

none

## Default

none

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

::: {#Nurdin1}
**(Nurdin)** Nurdin and Schotte Phys Rev E, 61(4), 3579 (2000)
:::