# 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/dof or extra or dynamic/dof or dynamic

extra/dof value = N
N = # of extra degrees of freedom to subtract
extra syntax is identical to extra/dof, will be disabled at some point
dynamic/dof value = yes or no
yes/no = do or do not re-compute the number of degrees of freedom (DOF) contributing to the temperature
dynamic syntax is identical to dynamic/dof, will be disabled at some point

## Examples

compute_modify myTemp extra/dof 0
compute_modify newtemp dynamic/dof yes extra/dof 600


## Description

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

The extra/dof or 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. For compute temp/partial, if one or more velocity components are excluded, the value used for extra is scaled accordingly. 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/dof or dynamic keyword determines whether the number of atoms N in the compute group and their associated degrees of freedom are re-computed each time a temperature is computed. Only compute styles that calculate a temperature use this option. By default, N and their DOF are assumed to be constant. If you are adding atoms or molecules to the system (see the fix pour, fix deposit, and fix gcmc commands) or expect atoms or molecules to be lost (e.g. due to exiting the simulation box or via fix evaporate), then this option should be used to insure the temperature is correctly normalized.

Note

The extra and dynamic keywords should not be used as they are deprecated (March 2017) and will eventually be disabled. Instead, use the equivalent extra/dof and dynamic/dof keywords.

none

## Default

The option defaults are extra/dof = 2 or 3 for 2d or 3d systems and dynamic/dof = no.