\(\renewcommand{\AA}{\text{Å}}\)

# compute improper/local command

## Syntax

    compute ID group-ID improper/local value1 value2 ...

- ID, group-ID are documented in compute command

- improper/local = style name of this compute command

- one or more values may be appended

- value = chi

      chi = tabulate improper angles

## Examples

    compute 1 all improper/local chi

## Description

Define a computation that calculates properties of individual improper interactions. The number of datums generated, aggregated across all processors, equals the number of impropers in the system, modified by the group parameter as explained below.

The value chi is the improper angle, as defined in the doc pages for the individual improper styles listed on improper_style doc page.

The local data stored by this command is generated by looping over all the atoms owned on a processor and their impropers. An improper will only be included if all four atoms in the improper are in the specified compute group.

Note that as atoms migrate from processor to processor, there will be no consistent ordering of the entries within the local vector or array from one timestep to the next. The only consistency that is guaranteed is that the ordering on a particular timestep will be the same for local vectors or arrays generated by other compute commands. For example, improper output from the compute property/local command can be combined with data from this command and output by the dump local command in a consistent way.

Here is an example of how to do this:

    compute 1 all property/local itype iatom1 iatom2 iatom3 iatom4
    compute 2 all improper/local chi
    dump 1 all local 1000 tmp.dump index c_1[1] c_1[2] c_1[3] c_1[4] c_1[5] c_2[1]

## Output info

This compute calculates a local vector or local array depending on the number of keywords. The length of the vector or number of rows in the array is the number of impropers. If a single keyword is specified, a local vector is produced. If two or more keywords are specified, a local array is produced where the number of columns = the number of keywords. The vector or array can be accessed by any command that uses local values from a compute as input. See the Howto output page for an overview of LAMMPS output options.

The output for chi will be in degrees.

## Restrictions

none

## Related commands

dump local, compute property/local

## Default

none