\(\renewcommand{\AA}{\text{Å}}\)

# 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 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

    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)) or diffusion with a source term (see Fig.1 in (Li2015)), as an analog of a periodic Poiseuille flow problem.

Deprecated since version 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 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. None of the 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. No parameter of these fixes can be used with the start/stop keywords of the run command. These fixes are not invoked during energy minimization.

## 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 page for more info.

Fix edpd/source must be used with the pair_style edpd command. Fix tdpd/source must be used with the pair_style tdpd command.

## Related commands

pair_style edpd, pair_style tdpd, compute edpd/temp/atom, compute tdpd/cc/atom

## Default

none

(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

(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