# fix edpd/source command

# fix tdpd/source command

## Syntax

    fix ID group-ID edpd/source keyword values ...
    fix ID group-ID tdpd/source cc_index keyword values ...

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

-   edpd/source or tdpd/source = style name of this fix command

-   index (only specified for tdpd/source) = index of chemical species
    (1 to Nspecies)

-   keyword = *sphere* or *cuboid* or *region*

        *sphere* args = cx cy cz radius source
          cx,cy,cz = x,y,z center of spherical domain (distance units)
          radius = radius of a spherical domain (distance units)
          source = heat source or concentration source (flux units, see below)
        *cuboid* values = cx cy cz dLx dLy dLz source
          cx,cy,cz = x,y,z center of a cuboid domain (distance units)
          dLx,dLy,dLz = x,y,z side length of a cuboid domain (distance units)
          source = heat source or concentration source (flux units, see below)
        *region* values = region-ID source
          region = ID of region for heat or concentration source
          source = heat source or concentration source (flux units, see below)

## Examples

``` LAMMPS
fix 1 all edpd/source sphere 0.0 0.0 0.0 5.0 0.01
fix 1 all edpd/source cuboid 0.0 0.0 0.0 20.0 10.0 10.0 -0.01
fix 1 all tdpd/source 1 sphere 5.0 0.0 0.0 5.0 0.01
fix 1 all tdpd/source 2 cuboid 0.0 0.0 0.0 20.0 10.0 10.0 0.01
fix 1 all tdpd/source 1 region lower -0.01
```

## Description

Fix *edpd/source* adds a heat source as an external heat flux to each
atom in a spherical or cuboid domain, where the *source* is in units of
energy/time. Fix *tdpd/source* adds an external concentration source of
the chemical species specified by *index* as an external concentration
flux for each atom in a spherical or cuboid domain, where the *source*
is in units of mole/volume/time.

This command can be used to give an additional heat/concentration source
term to atoms in a simulation, such as for a simulation of a heat
conduction with a source term (see Fig.12 in [(Li2014)](Li2014b)) or
diffusion with a source term (see Fig.1 in [(Li2015)](Li2015b)), as an
analog of a periodic Poiseuille flow problem.

::: deprecated
15Jun2023

The *sphere* and *cuboid* keywords will be removed in a future version
of LAMMPS. The same functionality and more can be achieved with a
region.
:::

If the *sphere* keyword is used, the *cx, cy, cz, radius* values define
a spherical domain to apply the source flux to.

If the *cuboid* keyword is used, the *cx, cy, cz, dLx, dLy, dLz* define
a cuboid domain to apply the source flux to.

If the *region* keyword is used, the *region-ID* selects which
[region](region) to apply the source flux to.

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

## Restart, fix_modify, output, run start/stop, minimize info

No information of these fixes is written to [binary restart
files](restart). None of the [fix_modify](fix_modify) options are
relevant to these fixes. No global or per-atom quantities are stored by
these fixes for access by various [output commands](Howto_output). No
parameter of these fixes can be used with the *start/stop* keywords of
the [run](run) command. These fixes are not invoked during [energy
minimization](minimize).

## Restrictions

These fixes are part of the DPD-MESO package. They are only enabled if
LAMMPS was built with that package. See the [Build
package](Build_package) page for more info.

Fix *edpd/source* must be used with the [pair_style edpd](pair_mesodpd)
command. Fix *tdpd/source* must be used with the [pair_style
tdpd](pair_mesodpd) command.

## Related commands

[pair_style edpd](pair_mesodpd), [pair_style tdpd](pair_mesodpd),
[compute edpd/temp/atom](compute_edpd_temp_atom), [compute
tdpd/cc/atom](compute_tdpd_cc_atom)

## Default

none

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

::: {#Li2014b}
**(Li2014)** Z. Li, Y.-H. Tang, H. Lei, B. Caswell and G.E. Karniadakis,
\"Energy-conserving dissipative particle dynamics with
temperature-dependent properties\", J. Comput. Phys., 265: 113-127
(2014). DOI: 10.1016/j.jcp.2014.02.003
:::

::: {#Li2015b}
**(Li2015)** Z. Li, A. Yazdani, A. Tartakovsky and G.E. Karniadakis,
\"Transport dissipative particle dynamics model for mesoscopic
advection-diffusion-reaction problems\", J. Chem. Phys., 143: 014101
(2015). DOI: 10.1063/1.4923254
:::