fix_modify AtC gradients command — LAMMPS documentation

\(\renewcommand{\AA}{\text{Å}}\)

# fix_modify AtC gradients command

## Syntax

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

- AtC fixID = ID of fix atc instance

- gradients = name of the AtC sub-command

- add or delete = select whether to add or delete calculation of gradients 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

    fix_modify AtC gradients add temperature velocity stress
    fix_modify AtC gradients delete velocity

## Description

Requests calculation and output of gradients of the fields from the AtC transfer class. These gradients will be with regard to spatial or material coordinate for Eulerian or Lagrangian analysis, respectively, as specified by fix_modify AtC atom_element_map

## Restrictions

Must be used with fix atc hardy.

## Related AtC commands

- fix_modify AtC command overview

- fix_modify AtC atom_element_map

- fix_modify AtC fields

- fix_modify AtC rates

## Default

None.

## References

(Eshelby) 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]