# fix_modify AtC kernel command

## Syntax

    fix_modify <AtC fixID> kernel <type> <parameters>

-   AtC fixID = ID of [fix atc](fix_atc) instance
-   kernel = name of the AtC sub-command
-   type = *step* or *cell* or *cubic_bar* or *cubic_cylinder* or
    *cubic_sphere* or *quartic_bar* or *quartic_cylinder* or
    *quartic_sphere*
-   the following parameter(s) are required for each kernel:
    -   *step* : \<radius\>
    -   *cell* : \<hx\> \<hy\> \<hz\> or \<h\>
    -   *cubic_bar* : \<half_width\>
    -   *cubic_cylinder* : \<radius\>
    -   *cubic_sphere* : \<radius\>
    -   *quartic_bar* : \<half_width\>
    -   *quartic_cylinder* : \<radius\>
    -   *quartic_sphere* : \<radius\>

## Examples

``` LAMMPS
fix_modify AtC kernel cell 1.0 1.0 1.0
fix_modify AtC kernel quartic_sphere 10.0
```

## Description

Sets the localization kernel type and parameters for [fix atc
hardy](fix_atc).

## Restrictions

Must be used with [fix atc hardy](fix_atc). For bar kernel types,
half-width oriented along x-direction. For cylinder kernel types,
cylindrical axis is assumed to be in z-direction.

## Related AtC commands

-   [fix_modify AtC command overview](atc_fix_modify)
-   [fix_modify AtC fields](atc_hardy_fields)
-   [fix_modify AtC gradients](atc_hardy_gradients)
-   [fix_modify AtC rates](atc_hardy_rates)
-   [fix_modify AtC computes](atc_hardy_computes)

## Default

None.