• one or more keyword/arg pairs may be listed
• keyword = collide or (react)

    collide arg = sc-ID
      sc-ID = ID of a surface collision model
    react arg = sr-ID
      sr-ID = ID of a surface reaction model or none 
  

Examples:

surf_modify sphere collide 1
surf_modify all collide sphere react sphere 

Description:

Set parameters for a group of surface elements in the specified group-ID. Surface elements are read in by the read_surf command. They can be assigned to groups by that command or via the group command.

The collide keyword is used to assign a surface collision model. Surface collision models are defined by the surf_collide command, which assigns each a surface collision ID, specified here as sc-ID.

The effect of this keyword is that particle collisions with surface elements in group-ID will be computed by the surface collision model with sc-ID.

The react keyword is used to assign a surface reaction model. Surface reaction models are defined by the surf_react command, which assigns each a surface reaction ID, specified here as sr-ID or the word "none". The latter means no reaction model.

The effect of this keyword is that particle collisions with surface elements in group-ID will induce reactions which are computed by the surface reaction model with sr-ID. If "none" is used, no surface reactions occur.

Note that if the same surface element is assigned to multiple groups, using this command multiple times may override the effect of a previous command that assigned a different collision or reaction model to a particular surface element.

Restrictions:

All surface elements must be assigned to a surface collision model via the collide keyword before a simlulation can be performed. Using a surface reaction model is optional.

This command cannot be used before surfaces exist.

Related commands:

read_surf, bound_modify

Default:

The default for surface reactions is none.