# compute_modify command

## Syntax

    compute_modify compute-ID keyword value ...

- compute-ID = ID of the compute to modify
- one or more keyword/value pairs may be listed
- keyword = extra or dynamic

    extra value = N
      N = # of extra degrees of freedom to subtract
    dynamic value = yes or no
      yes/no = do or do not recompute the number of atoms contributing to the temperature
    thermo value = yes or no
      yes/no = do or do not add contributions from fixes to the potential energy

## Examples

    compute_modify myTemp extra 0
    compute_modify newtemp dynamic yes extra 600

## Description

Modify one or more parameters of a previously defined compute. Not all compute styles support all parameters.

The extra keyword refers to how many degrees-of-freedom are subtracted (typically from 3N) as a normalizing factor in a temperature computation. Only computes that compute a temperature use this option. The default is 2 or 3 for 2d or 3d systems which is a correction factor for an ensemble of velocities with zero total linear momentum. You can use a negative number for the extra parameter if you need to add degrees-of-freedom. See the `compute temp/asphere` command for an example.

The dynamic keyword determines whether the number of atoms N in the compute group is re-computed each time a temperature is computed. Only compute styles that compute a temperature use this option. By default, N is assumed to be constant. If you are adding atoms to the system (see the `fix pour` or `fix deposit` commands) or expect atoms to be lost (e.g. due to evaporation), then this option can be used to insure the temperature is correctly normalized.

The thermo keyword determines whether the potential energy contribution calculated by some fixes is added to the potential energy calculated by the compute. Currently, only the compute of style pe uses this option. See the doc pages for individual fixes for details.

## Restrictions

> none

## Related commands

compute

## Default

The option defaults are extra = 2 or 3 for 2d or 3d systems and dynamic = no. Thermo is yes if the compute of style pe was defined with no extra keywords; otherwise it is no.