compute_modify command — LAMMPS documentation

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# 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 dynamic/dof

      extra/dof value = N
        N = # of extra degrees of freedom to subtract
      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

## 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 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/dof is scaled accordingly. You can use a negative number for the extra/dof parameter if you need to add degrees-of-freedom. See the compute temp/asphere command for an example.

The dynamic/dof keyword determines whether the number of atoms \(N\) in the compute group and their associated degrees of freedom (DOF) 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 ensure the temperature is correctly normalized.

## Restrictions

> none

## Related commands

compute

## Default

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