# fix_modify AtC rates command

## Syntax

    fix_modify <AtC fixID> rates <add|delete> <list_of_fields>

-   AtC fixID = ID of [fix atc](fix_atc) instance
-   rates = name of the AtC sub-command
-   *add* or *delete* = select whether to add or delete calculation of
    rates for 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 [\[Eshelby\]]()
    -   vacancy_concentration : volume fraction of vacancy content
    -   type_concentration : volume fraction of a specific atom type

## Examples

``` LAMMPS
fix_modify AtC rates add temperature velocity stress
fix_modify AtC rates delete stress
```

## Description

Requests calculation and output of rates (time derivatives) of the
fields from the AtC transfer class. For Eulerian analysis (see
[fix_modify AtC atom_element_map](atc_atom_element_map)) these rates are
the partial time derivatives of the nodal fields, not the full
(material) time derivatives.

## Restrictions

Must be used with [fix atc hardy](fix_atc).

## Related AtC commands

-   [fix_modify AtC command overview](atc_fix_modify)
-   [fix_modify AtC atom_element_map](atc_atom_element_map)
-   [fix_modify AtC fields](atc_hardy_fields)
-   [fix_modify AtC fields](atc_hardy_gradients)

## Default

None.