# fix_modify AtC fields command

## Syntax

    fix_modify <AtC fixID> fields <all|none>
    fix_modify <AtC fixID> fields <add|delete> <list_of_fields>

-   AtC fixID = ID of [fix atc](fix_atc) instance
-   fields = name of the AtC sub-command
-   *all* or *none* = output all or no fields
-   *add* or *delete* = add or delete the listed output fields
-   list_of_fields = one or more of the fields listed below:
    -   density : mass per unit volume
    -   displacement : displacement vector
    -   momentum : momentum per unit volume
    -   velocity : defined by momentum divided by density
    -   projected_velocity : simple kernel estimation of atomic
        velocities
    -   temperature : temperature derived from the relative atomic
        kinetic energy
    -   kinetic_temperature : temperature derived from the full kinetic
        energy
    -   number_density : simple kernel estimation of number of atoms per
        unit volume
    -   stress : Cauchy stress tensor for eulerian analysis
        (atom_element_map), or first Piola-Kirchhoff stress tensor for
        lagrangian analysis
    -   transformed_stress : first Piola-Kirchhoff stress tensor for
        eulerian analysis (atom_element_map), or Cauchy stress tensor
        for lagrangian analysis
    -   heat_flux : spatial heat flux vector for eulerian, or
        referential heat flux vector for lagrangian
    -   potential_energy : potential energy per unit volume
    -   kinetic_energy : kinetic energy per unit volume
    -   thermal_energy : thermal energy (kinetic energy - continuum
        kinetic energy) per unit volume
    -   internal_energy : total internal energy (potential + thermal)
        per unit volume
    -   energy : total energy (potential + kinetic) per unit volume
    -   number_density : number of atoms per unit volume
    -   eshelby_stress : configurational stress (energy-momentum) tensor
        defined by [\[Eshelby\]](#Eshelby){.citation}
    -   vacancy_concentration : volume fraction of vacancy content
    -   type_concentration : volume fraction of a specific atom type

## Examples

``` LAMMPS
fix_modify AtC fields add velocity temperature
```

## Description

Allows modification of the fields calculated and output by the AtC
transfer class. The commands are cumulative, e.g.:

``` LAMMPS
fix_modify AtC fields none
fix_modify AtC fields add velocity temperature
```

will only output the velocity and temperature fields.

## Restrictions

Must be used with [fix atc hardy](fix_atc). Currently, the stress and
heat flux formulas are only correct for central force potentials, e.g.
Lennard-Jones and EAM but not Stillinger-Weber.

## Related AtC commands

-   [fix_modify AtC command overview](atc_fix_modify)
-   [fix_modify AtC gradients](atc_hardy_gradients)
-   [fix_modify AtC rates](atc_hardy_rates)
-   [fix_modify AtC computes](atc_hardy_computes)

## Default

By default, no fields are output.

## References

::: {#citations}

[Eshelby]{#Eshelby .citation-label}

:   J.D. Eshelby, Philos. Trans. Royal Soc. London A, Math. Phys. Sci.,
    Vol. 244, No. 877 (1951) pp. 87-112; J. Elasticity, Vol. 5, Nos.
    3-4 (1975) pp. 321-335\]
:::